Georg Brandl | 68ee3a5 | 2008-03-25 07:21:32 +0000 | [diff] [blame] | 1 | .. XXX document all delegations to __special__ methods |
Georg Brandl | 116aa62 | 2007-08-15 14:28:22 +0000 | [diff] [blame] | 2 | .. _built-in-funcs: |
| 3 | |
| 4 | Built-in Functions |
| 5 | ================== |
| 6 | |
Georg Brandl | 4251481 | 2008-05-05 21:05:32 +0000 | [diff] [blame] | 7 | The Python interpreter has a number of functions and types built into it that |
| 8 | are always available. They are listed here in alphabetical order. |
Georg Brandl | 116aa62 | 2007-08-15 14:28:22 +0000 | [diff] [blame] | 9 | |
Ezio Melotti | f21c7ed | 2010-11-24 20:18:02 +0000 | [diff] [blame] | 10 | =================== ================= ================== ================ ==================== |
| 11 | .. .. Built-in Functions .. .. |
| 12 | =================== ================= ================== ================ ==================== |
Éric Araujo | 9edd9f0 | 2011-09-01 23:08:55 +0200 | [diff] [blame] | 13 | :func:`abs` |func-dict|_ :func:`help` :func:`min` :func:`setattr` |
Ezio Melotti | 1de9115 | 2010-11-28 04:18:54 +0000 | [diff] [blame] | 14 | :func:`all` :func:`dir` :func:`hex` :func:`next` :func:`slice` |
| 15 | :func:`any` :func:`divmod` :func:`id` :func:`object` :func:`sorted` |
| 16 | :func:`ascii` :func:`enumerate` :func:`input` :func:`oct` :func:`staticmethod` |
Chris Jerdonek | bb4e941 | 2012-11-28 01:38:40 -0800 | [diff] [blame] | 17 | :func:`bin` :func:`eval` :func:`int` :func:`open` |func-str|_ |
Ezio Melotti | 1de9115 | 2010-11-28 04:18:54 +0000 | [diff] [blame] | 18 | :func:`bool` :func:`exec` :func:`isinstance` :func:`ord` :func:`sum` |
| 19 | :func:`bytearray` :func:`filter` :func:`issubclass` :func:`pow` :func:`super` |
Nick Coghlan | 83c0ae5 | 2012-08-21 17:42:52 +1000 | [diff] [blame] | 20 | :func:`bytes` :func:`float` :func:`iter` :func:`print` |func-tuple|_ |
Ezio Melotti | 1de9115 | 2010-11-28 04:18:54 +0000 | [diff] [blame] | 21 | :func:`callable` :func:`format` :func:`len` :func:`property` :func:`type` |
Nick Coghlan | 83c0ae5 | 2012-08-21 17:42:52 +1000 | [diff] [blame] | 22 | :func:`chr` |func-frozenset|_ |func-list|_ |func-range|_ :func:`vars` |
Ezio Melotti | 17f9b3d | 2010-11-24 22:02:18 +0000 | [diff] [blame] | 23 | :func:`classmethod` :func:`getattr` :func:`locals` :func:`repr` :func:`zip` |
| 24 | :func:`compile` :func:`globals` :func:`map` :func:`reversed` :func:`__import__` |
| 25 | :func:`complex` :func:`hasattr` :func:`max` :func:`round` |
Éric Araujo | 9edd9f0 | 2011-09-01 23:08:55 +0200 | [diff] [blame] | 26 | :func:`delattr` :func:`hash` |func-memoryview|_ |func-set|_ |
Ezio Melotti | f21c7ed | 2010-11-24 20:18:02 +0000 | [diff] [blame] | 27 | =================== ================= ================== ================ ==================== |
Georg Brandl | 116aa62 | 2007-08-15 14:28:22 +0000 | [diff] [blame] | 28 | |
Éric Araujo | 9edd9f0 | 2011-09-01 23:08:55 +0200 | [diff] [blame] | 29 | .. using :func:`dict` would create a link to another page, so local targets are |
| 30 | used, with replacement texts to make the output in the table consistent |
| 31 | |
| 32 | .. |func-dict| replace:: ``dict()`` |
| 33 | .. |func-frozenset| replace:: ``frozenset()`` |
| 34 | .. |func-memoryview| replace:: ``memoryview()`` |
| 35 | .. |func-set| replace:: ``set()`` |
Nick Coghlan | 83c0ae5 | 2012-08-21 17:42:52 +1000 | [diff] [blame] | 36 | .. |func-list| replace:: ``list()`` |
Chris Jerdonek | bb4e941 | 2012-11-28 01:38:40 -0800 | [diff] [blame] | 37 | .. |func-str| replace:: ``str()`` |
Nick Coghlan | 83c0ae5 | 2012-08-21 17:42:52 +1000 | [diff] [blame] | 38 | .. |func-tuple| replace:: ``tuple()`` |
| 39 | .. |func-range| replace:: ``range()`` |
Éric Araujo | 9edd9f0 | 2011-09-01 23:08:55 +0200 | [diff] [blame] | 40 | |
| 41 | |
Georg Brandl | 116aa62 | 2007-08-15 14:28:22 +0000 | [diff] [blame] | 42 | .. function:: abs(x) |
| 43 | |
Georg Brandl | ba956ae | 2007-11-29 17:24:34 +0000 | [diff] [blame] | 44 | Return the absolute value of a number. The argument may be an |
Georg Brandl | 116aa62 | 2007-08-15 14:28:22 +0000 | [diff] [blame] | 45 | integer or a floating point number. If the argument is a complex number, its |
| 46 | magnitude is returned. |
| 47 | |
| 48 | |
| 49 | .. function:: all(iterable) |
| 50 | |
Georg Brandl | 0192bff | 2009-04-27 16:49:41 +0000 | [diff] [blame] | 51 | Return True if all elements of the *iterable* are true (or if the iterable |
| 52 | is empty). Equivalent to:: |
Georg Brandl | 116aa62 | 2007-08-15 14:28:22 +0000 | [diff] [blame] | 53 | |
| 54 | def all(iterable): |
| 55 | for element in iterable: |
| 56 | if not element: |
| 57 | return False |
| 58 | return True |
| 59 | |
Georg Brandl | 116aa62 | 2007-08-15 14:28:22 +0000 | [diff] [blame] | 60 | |
| 61 | .. function:: any(iterable) |
| 62 | |
Georg Brandl | 0192bff | 2009-04-27 16:49:41 +0000 | [diff] [blame] | 63 | Return True if any element of the *iterable* is true. If the iterable |
| 64 | is empty, return False. Equivalent to:: |
Georg Brandl | 116aa62 | 2007-08-15 14:28:22 +0000 | [diff] [blame] | 65 | |
| 66 | def any(iterable): |
| 67 | for element in iterable: |
| 68 | if element: |
| 69 | return True |
| 70 | return False |
| 71 | |
Georg Brandl | 116aa62 | 2007-08-15 14:28:22 +0000 | [diff] [blame] | 72 | |
Georg Brandl | 559e5d7 | 2008-06-11 18:37:52 +0000 | [diff] [blame] | 73 | .. function:: ascii(object) |
| 74 | |
| 75 | As :func:`repr`, return a string containing a printable representation of an |
| 76 | object, but escape the non-ASCII characters in the string returned by |
| 77 | :func:`repr` using ``\x``, ``\u`` or ``\U`` escapes. This generates a string |
| 78 | similar to that returned by :func:`repr` in Python 2. |
| 79 | |
| 80 | |
Georg Brandl | 116aa62 | 2007-08-15 14:28:22 +0000 | [diff] [blame] | 81 | .. function:: bin(x) |
| 82 | |
| 83 | Convert an integer number to a binary string. The result is a valid Python |
| 84 | expression. If *x* is not a Python :class:`int` object, it has to define an |
| 85 | :meth:`__index__` method that returns an integer. |
| 86 | |
Georg Brandl | 116aa62 | 2007-08-15 14:28:22 +0000 | [diff] [blame] | 87 | |
| 88 | .. function:: bool([x]) |
| 89 | |
Éric Araujo | 18ddf82 | 2011-09-01 23:10:36 +0200 | [diff] [blame] | 90 | Convert a value to a Boolean, using the standard :ref:`truth testing |
| 91 | procedure <truth>`. If *x* is false or omitted, this returns ``False``; |
| 92 | otherwise it returns ``True``. :class:`bool` is also a class, which is a |
| 93 | subclass of :class:`int` (see :ref:`typesnumeric`). Class :class:`bool` |
| 94 | cannot be subclassed further. Its only instances are ``False`` and |
| 95 | ``True`` (see :ref:`bltin-boolean-values`). |
Georg Brandl | 116aa62 | 2007-08-15 14:28:22 +0000 | [diff] [blame] | 96 | |
| 97 | .. index:: pair: Boolean; type |
| 98 | |
Georg Brandl | 116aa62 | 2007-08-15 14:28:22 +0000 | [diff] [blame] | 99 | |
Nick Coghlan | 83c0ae5 | 2012-08-21 17:42:52 +1000 | [diff] [blame] | 100 | .. _func-bytearray: |
Georg Brandl | 036490d | 2009-05-17 13:00:36 +0000 | [diff] [blame] | 101 | .. function:: bytearray([source[, encoding[, errors]]]) |
Georg Brandl | 85eb8c1 | 2007-08-31 16:33:38 +0000 | [diff] [blame] | 102 | |
Georg Brandl | 24eac03 | 2007-11-22 14:16:00 +0000 | [diff] [blame] | 103 | Return a new array of bytes. The :class:`bytearray` type is a mutable |
Georg Brandl | 9541463 | 2007-11-22 11:00:28 +0000 | [diff] [blame] | 104 | sequence of integers in the range 0 <= x < 256. It has most of the usual |
| 105 | methods of mutable sequences, described in :ref:`typesseq-mutable`, as well |
Antoine Pitrou | b85b3af | 2010-11-20 19:36:05 +0000 | [diff] [blame] | 106 | as most methods that the :class:`bytes` type has, see :ref:`bytes-methods`. |
Georg Brandl | 85eb8c1 | 2007-08-31 16:33:38 +0000 | [diff] [blame] | 107 | |
Georg Brandl | 036490d | 2009-05-17 13:00:36 +0000 | [diff] [blame] | 108 | The optional *source* parameter can be used to initialize the array in a few |
Georg Brandl | 85eb8c1 | 2007-08-31 16:33:38 +0000 | [diff] [blame] | 109 | different ways: |
| 110 | |
| 111 | * If it is a *string*, you must also give the *encoding* (and optionally, |
Georg Brandl | f694518 | 2008-02-01 11:56:49 +0000 | [diff] [blame] | 112 | *errors*) parameters; :func:`bytearray` then converts the string to |
Guido van Rossum | 98297ee | 2007-11-06 21:34:58 +0000 | [diff] [blame] | 113 | bytes using :meth:`str.encode`. |
Georg Brandl | 85eb8c1 | 2007-08-31 16:33:38 +0000 | [diff] [blame] | 114 | |
| 115 | * If it is an *integer*, the array will have that size and will be |
| 116 | initialized with null bytes. |
| 117 | |
| 118 | * If it is an object conforming to the *buffer* interface, a read-only buffer |
| 119 | of the object will be used to initialize the bytes array. |
| 120 | |
Guido van Rossum | 98297ee | 2007-11-06 21:34:58 +0000 | [diff] [blame] | 121 | * If it is an *iterable*, it must be an iterable of integers in the range |
| 122 | ``0 <= x < 256``, which are used as the initial contents of the array. |
Georg Brandl | 85eb8c1 | 2007-08-31 16:33:38 +0000 | [diff] [blame] | 123 | |
| 124 | Without an argument, an array of size 0 is created. |
| 125 | |
Chris Jerdonek | 006d907 | 2012-10-12 20:28:26 -0700 | [diff] [blame] | 126 | See also :ref:`binaryseq` and :ref:`typebytearray`. |
| 127 | |
Georg Brandl | 85eb8c1 | 2007-08-31 16:33:38 +0000 | [diff] [blame] | 128 | |
Nick Coghlan | 83c0ae5 | 2012-08-21 17:42:52 +1000 | [diff] [blame] | 129 | .. _func-bytes: |
Georg Brandl | 036490d | 2009-05-17 13:00:36 +0000 | [diff] [blame] | 130 | .. function:: bytes([source[, encoding[, errors]]]) |
Guido van Rossum | 98297ee | 2007-11-06 21:34:58 +0000 | [diff] [blame] | 131 | |
| 132 | Return a new "bytes" object, which is an immutable sequence of integers in |
| 133 | the range ``0 <= x < 256``. :class:`bytes` is an immutable version of |
Georg Brandl | 9541463 | 2007-11-22 11:00:28 +0000 | [diff] [blame] | 134 | :class:`bytearray` -- it has the same non-mutating methods and the same |
| 135 | indexing and slicing behavior. |
Georg Brandl | 48310cd | 2009-01-03 21:18:54 +0000 | [diff] [blame] | 136 | |
Georg Brandl | 476b355 | 2009-04-29 06:37:12 +0000 | [diff] [blame] | 137 | Accordingly, constructor arguments are interpreted as for :func:`bytearray`. |
Guido van Rossum | 98297ee | 2007-11-06 21:34:58 +0000 | [diff] [blame] | 138 | |
| 139 | Bytes objects can also be created with literals, see :ref:`strings`. |
| 140 | |
Chris Jerdonek | 006d907 | 2012-10-12 20:28:26 -0700 | [diff] [blame] | 141 | See also :ref:`binaryseq`, :ref:`typebytes`, and :ref:`bytes-methods`. |
| 142 | |
Guido van Rossum | 98297ee | 2007-11-06 21:34:58 +0000 | [diff] [blame] | 143 | |
Antoine Pitrou | e71362d | 2010-11-27 22:00:11 +0000 | [diff] [blame] | 144 | .. function:: callable(object) |
| 145 | |
| 146 | Return :const:`True` if the *object* argument appears callable, |
| 147 | :const:`False` if not. If this returns true, it is still possible that a |
| 148 | call fails, but if it is false, calling *object* will never succeed. |
| 149 | Note that classes are callable (calling a class returns a new instance); |
| 150 | instances are callable if their class has a :meth:`__call__` method. |
| 151 | |
| 152 | .. versionadded:: 3.2 |
| 153 | This function was first removed in Python 3.0 and then brought back |
| 154 | in Python 3.2. |
| 155 | |
| 156 | |
Georg Brandl | 116aa62 | 2007-08-15 14:28:22 +0000 | [diff] [blame] | 157 | .. function:: chr(i) |
| 158 | |
Alexander Belopolsky | 5d4dd3e | 2010-11-18 18:50:13 +0000 | [diff] [blame] | 159 | Return the string representing a character whose Unicode codepoint is the integer |
Georg Brandl | 85eb8c1 | 2007-08-31 16:33:38 +0000 | [diff] [blame] | 160 | *i*. For example, ``chr(97)`` returns the string ``'a'``. This is the |
Alexander Belopolsky | 5d4dd3e | 2010-11-18 18:50:13 +0000 | [diff] [blame] | 161 | inverse of :func:`ord`. The valid range for the argument is from 0 through |
| 162 | 1,114,111 (0x10FFFF in base 16). :exc:`ValueError` will be raised if *i* is |
| 163 | outside that range. |
| 164 | |
Georg Brandl | 116aa62 | 2007-08-15 14:28:22 +0000 | [diff] [blame] | 165 | |
| 166 | .. function:: classmethod(function) |
| 167 | |
| 168 | Return a class method for *function*. |
| 169 | |
| 170 | A class method receives the class as implicit first argument, just like an |
| 171 | instance method receives the instance. To declare a class method, use this |
| 172 | idiom:: |
| 173 | |
| 174 | class C: |
| 175 | @classmethod |
| 176 | def f(cls, arg1, arg2, ...): ... |
| 177 | |
Christian Heimes | d8654cf | 2007-12-02 15:22:16 +0000 | [diff] [blame] | 178 | The ``@classmethod`` form is a function :term:`decorator` -- see the description |
| 179 | of function definitions in :ref:`function` for details. |
Georg Brandl | 116aa62 | 2007-08-15 14:28:22 +0000 | [diff] [blame] | 180 | |
| 181 | It can be called either on the class (such as ``C.f()``) or on an instance (such |
| 182 | as ``C().f()``). The instance is ignored except for its class. If a class |
| 183 | method is called for a derived class, the derived class object is passed as the |
| 184 | implied first argument. |
| 185 | |
| 186 | Class methods are different than C++ or Java static methods. If you want those, |
| 187 | see :func:`staticmethod` in this section. |
| 188 | |
| 189 | For more information on class methods, consult the documentation on the standard |
| 190 | type hierarchy in :ref:`types`. |
| 191 | |
Georg Brandl | 116aa62 | 2007-08-15 14:28:22 +0000 | [diff] [blame] | 192 | |
Georg Brandl | 8334fd9 | 2010-12-04 10:26:46 +0000 | [diff] [blame] | 193 | .. function:: compile(source, filename, mode, flags=0, dont_inherit=False, optimize=-1) |
Georg Brandl | 116aa62 | 2007-08-15 14:28:22 +0000 | [diff] [blame] | 194 | |
Benjamin Peterson | ec9199b | 2008-11-08 17:05:00 +0000 | [diff] [blame] | 195 | Compile the *source* into a code or AST object. Code objects can be executed |
Ezio Melotti | 6e40e27 | 2010-01-04 09:29:10 +0000 | [diff] [blame] | 196 | by :func:`exec` or :func:`eval`. *source* can either be a string or an AST |
Benjamin Peterson | 45abfbc | 2009-12-13 00:32:14 +0000 | [diff] [blame] | 197 | object. Refer to the :mod:`ast` module documentation for information on how |
| 198 | to work with AST objects. |
Georg Brandl | 116aa62 | 2007-08-15 14:28:22 +0000 | [diff] [blame] | 199 | |
Benjamin Peterson | ec9199b | 2008-11-08 17:05:00 +0000 | [diff] [blame] | 200 | The *filename* argument should give the file from which the code was read; |
| 201 | pass some recognizable value if it wasn't read from a file (``'<string>'`` is |
| 202 | commonly used). |
| 203 | |
| 204 | The *mode* argument specifies what kind of code must be compiled; it can be |
| 205 | ``'exec'`` if *source* consists of a sequence of statements, ``'eval'`` if it |
| 206 | consists of a single expression, or ``'single'`` if it consists of a single |
| 207 | interactive statement (in the latter case, expression statements that |
R. David Murray | 6601126 | 2009-06-25 17:37:57 +0000 | [diff] [blame] | 208 | evaluate to something other than ``None`` will be printed). |
Georg Brandl | 116aa62 | 2007-08-15 14:28:22 +0000 | [diff] [blame] | 209 | |
Georg Brandl | e06de8b | 2008-05-05 21:42:51 +0000 | [diff] [blame] | 210 | The optional arguments *flags* and *dont_inherit* control which future |
| 211 | statements (see :pep:`236`) affect the compilation of *source*. If neither |
| 212 | is present (or both are zero) the code is compiled with those future |
| 213 | statements that are in effect in the code that is calling compile. If the |
| 214 | *flags* argument is given and *dont_inherit* is not (or is zero) then the |
Georg Brandl | 116aa62 | 2007-08-15 14:28:22 +0000 | [diff] [blame] | 215 | future statements specified by the *flags* argument are used in addition to |
| 216 | those that would be used anyway. If *dont_inherit* is a non-zero integer then |
Georg Brandl | e06de8b | 2008-05-05 21:42:51 +0000 | [diff] [blame] | 217 | the *flags* argument is it -- the future statements in effect around the call |
| 218 | to compile are ignored. |
Georg Brandl | 116aa62 | 2007-08-15 14:28:22 +0000 | [diff] [blame] | 219 | |
Christian Heimes | faf2f63 | 2008-01-06 16:59:19 +0000 | [diff] [blame] | 220 | Future statements are specified by bits which can be bitwise ORed together to |
Georg Brandl | 116aa62 | 2007-08-15 14:28:22 +0000 | [diff] [blame] | 221 | specify multiple statements. The bitfield required to specify a given feature |
| 222 | can be found as the :attr:`compiler_flag` attribute on the :class:`_Feature` |
| 223 | instance in the :mod:`__future__` module. |
| 224 | |
Georg Brandl | 8334fd9 | 2010-12-04 10:26:46 +0000 | [diff] [blame] | 225 | The argument *optimize* specifies the optimization level of the compiler; the |
| 226 | default value of ``-1`` selects the optimization level of the interpreter as |
| 227 | given by :option:`-O` options. Explicit levels are ``0`` (no optimization; |
| 228 | ``__debug__`` is true), ``1`` (asserts are removed, ``__debug__`` is false) |
| 229 | or ``2`` (docstrings are removed too). |
| 230 | |
Christian Heimes | 7f04431 | 2008-01-06 17:05:40 +0000 | [diff] [blame] | 231 | This function raises :exc:`SyntaxError` if the compiled source is invalid, |
| 232 | and :exc:`TypeError` if the source contains null bytes. |
| 233 | |
Benjamin Peterson | ec9199b | 2008-11-08 17:05:00 +0000 | [diff] [blame] | 234 | .. note:: |
| 235 | |
Benjamin Peterson | 2021100 | 2009-11-25 18:34:42 +0000 | [diff] [blame] | 236 | When compiling a string with multi-line code in ``'single'`` or |
Benjamin Peterson | aeaa592 | 2009-11-13 00:17:59 +0000 | [diff] [blame] | 237 | ``'eval'`` mode, input must be terminated by at least one newline |
| 238 | character. This is to facilitate detection of incomplete and complete |
| 239 | statements in the :mod:`code` module. |
| 240 | |
Benjamin Peterson | aeaa592 | 2009-11-13 00:17:59 +0000 | [diff] [blame] | 241 | .. versionchanged:: 3.2 |
| 242 | Allowed use of Windows and Mac newlines. Also input in ``'exec'`` mode |
Georg Brandl | 8334fd9 | 2010-12-04 10:26:46 +0000 | [diff] [blame] | 243 | does not have to end in a newline anymore. Added the *optimize* parameter. |
Benjamin Peterson | ec9199b | 2008-11-08 17:05:00 +0000 | [diff] [blame] | 244 | |
Georg Brandl | 116aa62 | 2007-08-15 14:28:22 +0000 | [diff] [blame] | 245 | |
| 246 | .. function:: complex([real[, imag]]) |
| 247 | |
| 248 | Create a complex number with the value *real* + *imag*\*j or convert a string or |
| 249 | number to a complex number. If the first parameter is a string, it will be |
| 250 | interpreted as a complex number and the function must be called without a second |
| 251 | parameter. The second parameter can never be a string. Each argument may be any |
| 252 | numeric type (including complex). If *imag* is omitted, it defaults to zero and |
Georg Brandl | 5c10664 | 2007-11-29 17:41:05 +0000 | [diff] [blame] | 253 | the function serves as a numeric conversion function like :func:`int` |
| 254 | and :func:`float`. If both arguments are omitted, returns ``0j``. |
Georg Brandl | 116aa62 | 2007-08-15 14:28:22 +0000 | [diff] [blame] | 255 | |
Mark Dickinson | 328dd0d | 2012-03-10 16:09:35 +0000 | [diff] [blame] | 256 | .. note:: |
| 257 | |
| 258 | When converting from a string, the string must not contain whitespace |
| 259 | around the central ``+`` or ``-`` operator. For example, |
| 260 | ``complex('1+2j')`` is fine, but ``complex('1 + 2j')`` raises |
| 261 | :exc:`ValueError`. |
| 262 | |
Georg Brandl | 116aa62 | 2007-08-15 14:28:22 +0000 | [diff] [blame] | 263 | The complex type is described in :ref:`typesnumeric`. |
| 264 | |
| 265 | |
| 266 | .. function:: delattr(object, name) |
| 267 | |
| 268 | This is a relative of :func:`setattr`. The arguments are an object and a |
| 269 | string. The string must be the name of one of the object's attributes. The |
| 270 | function deletes the named attribute, provided the object allows it. For |
| 271 | example, ``delattr(x, 'foobar')`` is equivalent to ``del x.foobar``. |
| 272 | |
| 273 | |
Éric Araujo | 9edd9f0 | 2011-09-01 23:08:55 +0200 | [diff] [blame] | 274 | .. _func-dict: |
Chris Jerdonek | f341317 | 2012-10-13 03:22:33 -0700 | [diff] [blame] | 275 | .. function:: dict(**kwarg) |
| 276 | dict(mapping, **kwarg) |
| 277 | dict(iterable, **kwarg) |
Georg Brandl | 116aa62 | 2007-08-15 14:28:22 +0000 | [diff] [blame] | 278 | :noindex: |
| 279 | |
Chris Jerdonek | f341317 | 2012-10-13 03:22:33 -0700 | [diff] [blame] | 280 | Create a new dictionary. The :class:`dict` object is the dictionary class. |
| 281 | See :class:`dict` and :ref:`typesmapping` for documentation about this |
| 282 | class. |
Georg Brandl | 116aa62 | 2007-08-15 14:28:22 +0000 | [diff] [blame] | 283 | |
Chris Jerdonek | f341317 | 2012-10-13 03:22:33 -0700 | [diff] [blame] | 284 | For other containers see the built-in :class:`list`, :class:`set`, and |
| 285 | :class:`tuple` classes, as well as the :mod:`collections` module. |
Georg Brandl | 116aa62 | 2007-08-15 14:28:22 +0000 | [diff] [blame] | 286 | |
| 287 | |
| 288 | .. function:: dir([object]) |
| 289 | |
| 290 | Without arguments, return the list of names in the current local scope. With an |
| 291 | argument, attempt to return a list of valid attributes for that object. |
| 292 | |
| 293 | If the object has a method named :meth:`__dir__`, this method will be called and |
| 294 | must return the list of attributes. This allows objects that implement a custom |
| 295 | :func:`__getattr__` or :func:`__getattribute__` function to customize the way |
| 296 | :func:`dir` reports their attributes. |
| 297 | |
| 298 | If the object does not provide :meth:`__dir__`, the function tries its best to |
| 299 | gather information from the object's :attr:`__dict__` attribute, if defined, and |
| 300 | from its type object. The resulting list is not necessarily complete, and may |
| 301 | be inaccurate when the object has a custom :func:`__getattr__`. |
| 302 | |
| 303 | The default :func:`dir` mechanism behaves differently with different types of |
| 304 | objects, as it attempts to produce the most relevant, rather than complete, |
| 305 | information: |
| 306 | |
| 307 | * If the object is a module object, the list contains the names of the module's |
| 308 | attributes. |
| 309 | |
| 310 | * If the object is a type or class object, the list contains the names of its |
| 311 | attributes, and recursively of the attributes of its bases. |
| 312 | |
| 313 | * Otherwise, the list contains the object's attributes' names, the names of its |
| 314 | class's attributes, and recursively of the attributes of its class's base |
| 315 | classes. |
| 316 | |
Christian Heimes | fe337bf | 2008-03-23 21:54:12 +0000 | [diff] [blame] | 317 | The resulting list is sorted alphabetically. For example: |
| 318 | |
| 319 | >>> import struct |
Raymond Hettinger | 9028928 | 2011-06-01 16:17:23 -0700 | [diff] [blame] | 320 | >>> dir() # show the names in the module namespace |
Andrew Svetlov | 439e17f | 2012-08-12 15:16:42 +0300 | [diff] [blame] | 321 | ['__builtins__', '__name__', 'struct'] |
| 322 | >>> dir(struct) # show the names in the struct module # doctest: +SKIP |
| 323 | ['Struct', '__all__', '__builtins__', '__cached__', '__doc__', '__file__', |
| 324 | '__initializing__', '__loader__', '__name__', '__package__', |
| 325 | '_clearcache', 'calcsize', 'error', 'pack', 'pack_into', |
Christian Heimes | fe337bf | 2008-03-23 21:54:12 +0000 | [diff] [blame] | 326 | 'unpack', 'unpack_from'] |
Raymond Hettinger | 9028928 | 2011-06-01 16:17:23 -0700 | [diff] [blame] | 327 | >>> class Shape(object): |
Andrew Svetlov | 439e17f | 2012-08-12 15:16:42 +0300 | [diff] [blame] | 328 | ... def __dir__(self): |
| 329 | ... return ['area', 'perimeter', 'location'] |
Raymond Hettinger | 9028928 | 2011-06-01 16:17:23 -0700 | [diff] [blame] | 330 | >>> s = Shape() |
| 331 | >>> dir(s) |
Andrew Svetlov | 439e17f | 2012-08-12 15:16:42 +0300 | [diff] [blame] | 332 | ['area', 'location', 'perimeter'] |
Georg Brandl | 116aa62 | 2007-08-15 14:28:22 +0000 | [diff] [blame] | 333 | |
| 334 | .. note:: |
| 335 | |
| 336 | Because :func:`dir` is supplied primarily as a convenience for use at an |
Georg Brandl | 036490d | 2009-05-17 13:00:36 +0000 | [diff] [blame] | 337 | interactive prompt, it tries to supply an interesting set of names more |
| 338 | than it tries to supply a rigorously or consistently defined set of names, |
| 339 | and its detailed behavior may change across releases. For example, |
| 340 | metaclass attributes are not in the result list when the argument is a |
| 341 | class. |
Georg Brandl | 116aa62 | 2007-08-15 14:28:22 +0000 | [diff] [blame] | 342 | |
| 343 | |
| 344 | .. function:: divmod(a, b) |
| 345 | |
| 346 | Take two (non complex) numbers as arguments and return a pair of numbers |
Georg Brandl | 036490d | 2009-05-17 13:00:36 +0000 | [diff] [blame] | 347 | consisting of their quotient and remainder when using integer division. With |
| 348 | mixed operand types, the rules for binary arithmetic operators apply. For |
| 349 | integers, the result is the same as ``(a // b, a % b)``. For floating point |
| 350 | numbers the result is ``(q, a % b)``, where *q* is usually ``math.floor(a / |
| 351 | b)`` but may be 1 less than that. In any case ``q * b + a % b`` is very |
| 352 | close to *a*, if ``a % b`` is non-zero it has the same sign as *b*, and ``0 |
| 353 | <= abs(a % b) < abs(b)``. |
Georg Brandl | 116aa62 | 2007-08-15 14:28:22 +0000 | [diff] [blame] | 354 | |
Georg Brandl | 116aa62 | 2007-08-15 14:28:22 +0000 | [diff] [blame] | 355 | |
Georg Brandl | 036490d | 2009-05-17 13:00:36 +0000 | [diff] [blame] | 356 | .. function:: enumerate(iterable, start=0) |
Georg Brandl | 116aa62 | 2007-08-15 14:28:22 +0000 | [diff] [blame] | 357 | |
Georg Brandl | d11ae5d | 2008-05-16 13:27:32 +0000 | [diff] [blame] | 358 | Return an enumerate object. *iterable* must be a sequence, an |
Ezio Melotti | 7fa8222 | 2012-10-12 13:42:08 +0300 | [diff] [blame] | 359 | :term:`iterator`, or some other object which supports iteration. |
| 360 | The :meth:`~iterator.__next__` method of the iterator returned by |
| 361 | :func:`enumerate` returns a tuple containing a count (from *start* which |
| 362 | defaults to 0) and the values obtained from iterating over *iterable*. |
Georg Brandl | 116aa62 | 2007-08-15 14:28:22 +0000 | [diff] [blame] | 363 | |
Raymond Hettinger | 9d3df6d | 2011-06-25 15:00:14 +0200 | [diff] [blame] | 364 | >>> seasons = ['Spring', 'Summer', 'Fall', 'Winter'] |
| 365 | >>> list(enumerate(seasons)) |
| 366 | [(0, 'Spring'), (1, 'Summer'), (2, 'Fall'), (3, 'Winter')] |
| 367 | >>> list(enumerate(seasons, start=1)) |
| 368 | [(1, 'Spring'), (2, 'Summer'), (3, 'Fall'), (4, 'Winter')] |
Raymond Hettinger | 9028928 | 2011-06-01 16:17:23 -0700 | [diff] [blame] | 369 | |
| 370 | Equivalent to:: |
| 371 | |
| 372 | def enumerate(sequence, start=0): |
| 373 | n = start |
| 374 | for elem in sequence: |
| 375 | yield n, elem |
| 376 | n += 1 |
Georg Brandl | 116aa62 | 2007-08-15 14:28:22 +0000 | [diff] [blame] | 377 | |
Georg Brandl | 116aa62 | 2007-08-15 14:28:22 +0000 | [diff] [blame] | 378 | |
Georg Brandl | 036490d | 2009-05-17 13:00:36 +0000 | [diff] [blame] | 379 | .. function:: eval(expression, globals=None, locals=None) |
Georg Brandl | 116aa62 | 2007-08-15 14:28:22 +0000 | [diff] [blame] | 380 | |
| 381 | The arguments are a string and optional globals and locals. If provided, |
| 382 | *globals* must be a dictionary. If provided, *locals* can be any mapping |
| 383 | object. |
| 384 | |
Georg Brandl | 116aa62 | 2007-08-15 14:28:22 +0000 | [diff] [blame] | 385 | The *expression* argument is parsed and evaluated as a Python expression |
| 386 | (technically speaking, a condition list) using the *globals* and *locals* |
Georg Brandl | 9afde1c | 2007-11-01 20:32:30 +0000 | [diff] [blame] | 387 | dictionaries as global and local namespace. If the *globals* dictionary is |
Georg Brandl | 116aa62 | 2007-08-15 14:28:22 +0000 | [diff] [blame] | 388 | present and lacks '__builtins__', the current globals are copied into *globals* |
| 389 | before *expression* is parsed. This means that *expression* normally has full |
Georg Brandl | 1a3284e | 2007-12-02 09:40:06 +0000 | [diff] [blame] | 390 | access to the standard :mod:`builtins` module and restricted environments are |
Georg Brandl | 116aa62 | 2007-08-15 14:28:22 +0000 | [diff] [blame] | 391 | propagated. If the *locals* dictionary is omitted it defaults to the *globals* |
| 392 | dictionary. If both dictionaries are omitted, the expression is executed in the |
Christian Heimes | 5b5e81c | 2007-12-31 16:14:33 +0000 | [diff] [blame] | 393 | environment where :func:`eval` is called. The return value is the result of |
Christian Heimes | fe337bf | 2008-03-23 21:54:12 +0000 | [diff] [blame] | 394 | the evaluated expression. Syntax errors are reported as exceptions. Example: |
Georg Brandl | 116aa62 | 2007-08-15 14:28:22 +0000 | [diff] [blame] | 395 | |
| 396 | >>> x = 1 |
Georg Brandl | 6911e3c | 2007-09-04 07:15:32 +0000 | [diff] [blame] | 397 | >>> eval('x+1') |
Georg Brandl | 116aa62 | 2007-08-15 14:28:22 +0000 | [diff] [blame] | 398 | 2 |
| 399 | |
Benjamin Peterson | 3e4f055 | 2008-09-02 00:31:15 +0000 | [diff] [blame] | 400 | This function can also be used to execute arbitrary code objects (such as |
| 401 | those created by :func:`compile`). In this case pass a code object instead |
| 402 | of a string. If the code object has been compiled with ``'exec'`` as the |
Georg Brandl | 1f70cdf | 2010-03-21 09:04:24 +0000 | [diff] [blame] | 403 | *mode* argument, :func:`eval`\'s return value will be ``None``. |
Georg Brandl | 116aa62 | 2007-08-15 14:28:22 +0000 | [diff] [blame] | 404 | |
| 405 | Hints: dynamic execution of statements is supported by the :func:`exec` |
| 406 | function. The :func:`globals` and :func:`locals` functions |
| 407 | returns the current global and local dictionary, respectively, which may be |
| 408 | useful to pass around for use by :func:`eval` or :func:`exec`. |
| 409 | |
Georg Brandl | 05bfcc5 | 2010-07-11 09:42:10 +0000 | [diff] [blame] | 410 | See :func:`ast.literal_eval` for a function that can safely evaluate strings |
| 411 | with expressions containing only literals. |
| 412 | |
Georg Brandl | 116aa62 | 2007-08-15 14:28:22 +0000 | [diff] [blame] | 413 | |
| 414 | .. function:: exec(object[, globals[, locals]]) |
| 415 | |
Benjamin Peterson | d3013ff | 2008-11-11 21:43:42 +0000 | [diff] [blame] | 416 | This function supports dynamic execution of Python code. *object* must be |
| 417 | either a string or a code object. If it is a string, the string is parsed as |
| 418 | a suite of Python statements which is then executed (unless a syntax error |
Georg Brandl | 47f27a3 | 2009-03-31 16:57:13 +0000 | [diff] [blame] | 419 | occurs). [#]_ If it is a code object, it is simply executed. In all cases, |
| 420 | the code that's executed is expected to be valid as file input (see the |
| 421 | section "File input" in the Reference Manual). Be aware that the |
| 422 | :keyword:`return` and :keyword:`yield` statements may not be used outside of |
| 423 | function definitions even within the context of code passed to the |
| 424 | :func:`exec` function. The return value is ``None``. |
Georg Brandl | 116aa62 | 2007-08-15 14:28:22 +0000 | [diff] [blame] | 425 | |
| 426 | In all cases, if the optional parts are omitted, the code is executed in the |
| 427 | current scope. If only *globals* is provided, it must be a dictionary, which |
| 428 | will be used for both the global and the local variables. If *globals* and |
| 429 | *locals* are given, they are used for the global and local variables, |
Terry Jan Reedy | 83efd6c | 2012-07-08 17:36:14 -0400 | [diff] [blame] | 430 | respectively. If provided, *locals* can be any mapping object. Remember |
| 431 | that at module level, globals and locals are the same dictionary. If exec |
| 432 | gets two separate objects as *globals* and *locals*, the code will be |
| 433 | executed as if it were embedded in a class definition. |
Georg Brandl | 116aa62 | 2007-08-15 14:28:22 +0000 | [diff] [blame] | 434 | |
| 435 | If the *globals* dictionary does not contain a value for the key |
| 436 | ``__builtins__``, a reference to the dictionary of the built-in module |
Georg Brandl | 1a3284e | 2007-12-02 09:40:06 +0000 | [diff] [blame] | 437 | :mod:`builtins` is inserted under that key. That way you can control what |
Georg Brandl | 116aa62 | 2007-08-15 14:28:22 +0000 | [diff] [blame] | 438 | builtins are available to the executed code by inserting your own |
| 439 | ``__builtins__`` dictionary into *globals* before passing it to :func:`exec`. |
| 440 | |
| 441 | .. note:: |
| 442 | |
| 443 | The built-in functions :func:`globals` and :func:`locals` return the current |
| 444 | global and local dictionary, respectively, which may be useful to pass around |
| 445 | for use as the second and third argument to :func:`exec`. |
| 446 | |
Georg Brandl | e720c0a | 2009-04-27 16:20:50 +0000 | [diff] [blame] | 447 | .. note:: |
Georg Brandl | 116aa62 | 2007-08-15 14:28:22 +0000 | [diff] [blame] | 448 | |
| 449 | The default *locals* act as described for function :func:`locals` below: |
Georg Brandl | f694518 | 2008-02-01 11:56:49 +0000 | [diff] [blame] | 450 | modifications to the default *locals* dictionary should not be attempted. |
| 451 | Pass an explicit *locals* dictionary if you need to see effects of the |
| 452 | code on *locals* after function :func:`exec` returns. |
Georg Brandl | 116aa62 | 2007-08-15 14:28:22 +0000 | [diff] [blame] | 453 | |
| 454 | |
| 455 | .. function:: filter(function, iterable) |
| 456 | |
Georg Brandl | 952aea2 | 2007-09-04 17:50:40 +0000 | [diff] [blame] | 457 | Construct an iterator from those elements of *iterable* for which *function* |
| 458 | returns true. *iterable* may be either a sequence, a container which |
Georg Brandl | 9afde1c | 2007-11-01 20:32:30 +0000 | [diff] [blame] | 459 | supports iteration, or an iterator. If *function* is ``None``, the identity |
| 460 | function is assumed, that is, all elements of *iterable* that are false are |
| 461 | removed. |
Georg Brandl | 116aa62 | 2007-08-15 14:28:22 +0000 | [diff] [blame] | 462 | |
Georg Brandl | 952aea2 | 2007-09-04 17:50:40 +0000 | [diff] [blame] | 463 | Note that ``filter(function, iterable)`` is equivalent to the generator |
| 464 | expression ``(item for item in iterable if function(item))`` if function is |
| 465 | not ``None`` and ``(item for item in iterable if item)`` if function is |
| 466 | ``None``. |
Georg Brandl | 116aa62 | 2007-08-15 14:28:22 +0000 | [diff] [blame] | 467 | |
Raymond Hettinger | cdf8ba3 | 2009-02-19 04:45:07 +0000 | [diff] [blame] | 468 | See :func:`itertools.filterfalse` for the complementary function that returns |
| 469 | elements of *iterable* for which *function* returns false. |
| 470 | |
Georg Brandl | 116aa62 | 2007-08-15 14:28:22 +0000 | [diff] [blame] | 471 | |
| 472 | .. function:: float([x]) |
| 473 | |
Mark Dickinson | 47c74ac | 2010-11-21 21:09:58 +0000 | [diff] [blame] | 474 | .. index:: |
| 475 | single: NaN |
| 476 | single: Infinity |
Georg Brandl | 116aa62 | 2007-08-15 14:28:22 +0000 | [diff] [blame] | 477 | |
Mark Dickinson | 47c74ac | 2010-11-21 21:09:58 +0000 | [diff] [blame] | 478 | Convert a string or a number to floating point. |
Georg Brandl | 116aa62 | 2007-08-15 14:28:22 +0000 | [diff] [blame] | 479 | |
Mark Dickinson | 47c74ac | 2010-11-21 21:09:58 +0000 | [diff] [blame] | 480 | If the argument is a string, it should contain a decimal number, optionally |
| 481 | preceded by a sign, and optionally embedded in whitespace. The optional |
| 482 | sign may be ``'+'`` or ``'-'``; a ``'+'`` sign has no effect on the value |
| 483 | produced. The argument may also be a string representing a NaN |
| 484 | (not-a-number), or a positive or negative infinity. More precisely, the |
| 485 | input must conform to the following grammar after leading and trailing |
| 486 | whitespace characters are removed: |
Georg Brandl | 116aa62 | 2007-08-15 14:28:22 +0000 | [diff] [blame] | 487 | |
Mark Dickinson | 47c74ac | 2010-11-21 21:09:58 +0000 | [diff] [blame] | 488 | .. productionlist:: |
| 489 | sign: "+" | "-" |
| 490 | infinity: "Infinity" | "inf" |
| 491 | nan: "nan" |
Georg Brandl | 4640237 | 2010-12-04 19:06:18 +0000 | [diff] [blame] | 492 | numeric_value: `floatnumber` | `infinity` | `nan` |
| 493 | numeric_string: [`sign`] `numeric_value` |
Mark Dickinson | 47c74ac | 2010-11-21 21:09:58 +0000 | [diff] [blame] | 494 | |
| 495 | Here ``floatnumber`` is the form of a Python floating-point literal, |
| 496 | described in :ref:`floating`. Case is not significant, so, for example, |
| 497 | "inf", "Inf", "INFINITY" and "iNfINity" are all acceptable spellings for |
| 498 | positive infinity. |
| 499 | |
| 500 | Otherwise, if the argument is an integer or a floating point number, a |
| 501 | floating point number with the same value (within Python's floating point |
| 502 | precision) is returned. If the argument is outside the range of a Python |
| 503 | float, an :exc:`OverflowError` will be raised. |
| 504 | |
| 505 | For a general Python object ``x``, ``float(x)`` delegates to |
| 506 | ``x.__float__()``. |
| 507 | |
| 508 | If no argument is given, ``0.0`` is returned. |
| 509 | |
| 510 | Examples:: |
| 511 | |
| 512 | >>> float('+1.23') |
| 513 | 1.23 |
| 514 | >>> float(' -12345\n') |
| 515 | -12345.0 |
| 516 | >>> float('1e-003') |
| 517 | 0.001 |
| 518 | >>> float('+1E6') |
| 519 | 1000000.0 |
| 520 | >>> float('-Infinity') |
| 521 | -inf |
Georg Brandl | 116aa62 | 2007-08-15 14:28:22 +0000 | [diff] [blame] | 522 | |
| 523 | The float type is described in :ref:`typesnumeric`. |
| 524 | |
Chris Jerdonek | bb4e941 | 2012-11-28 01:38:40 -0800 | [diff] [blame] | 525 | .. index:: |
| 526 | single: __format__ |
| 527 | single: string; format() (built-in function) |
| 528 | |
Éric Araujo | 9edd9f0 | 2011-09-01 23:08:55 +0200 | [diff] [blame] | 529 | |
Georg Brandl | 4b49131 | 2007-08-31 09:22:56 +0000 | [diff] [blame] | 530 | .. function:: format(value[, format_spec]) |
| 531 | |
Georg Brandl | 5579ba9 | 2009-02-23 10:24:05 +0000 | [diff] [blame] | 532 | Convert a *value* to a "formatted" representation, as controlled by |
| 533 | *format_spec*. The interpretation of *format_spec* will depend on the type |
| 534 | of the *value* argument, however there is a standard formatting syntax that |
| 535 | is used by most built-in types: :ref:`formatspec`. |
Georg Brandl | 48310cd | 2009-01-03 21:18:54 +0000 | [diff] [blame] | 536 | |
Raymond Hettinger | 30439b2 | 2011-05-11 10:47:27 -0700 | [diff] [blame] | 537 | The default *format_spec* is an empty string which usually gives the same |
Chris Jerdonek | 5fae0e5 | 2012-11-20 17:45:51 -0800 | [diff] [blame] | 538 | effect as calling :func:`str(value) <str>`. |
Georg Brandl | 4b49131 | 2007-08-31 09:22:56 +0000 | [diff] [blame] | 539 | |
Raymond Hettinger | 30439b2 | 2011-05-11 10:47:27 -0700 | [diff] [blame] | 540 | A call to ``format(value, format_spec)`` is translated to |
| 541 | ``type(value).__format__(format_spec)`` which bypasses the instance |
| 542 | dictionary when searching for the value's :meth:`__format__` method. A |
| 543 | :exc:`TypeError` exception is raised if the method is not found or if either |
| 544 | the *format_spec* or the return value are not strings. |
Georg Brandl | 4b49131 | 2007-08-31 09:22:56 +0000 | [diff] [blame] | 545 | |
Éric Araujo | 9edd9f0 | 2011-09-01 23:08:55 +0200 | [diff] [blame] | 546 | |
| 547 | .. _func-frozenset: |
Georg Brandl | 116aa62 | 2007-08-15 14:28:22 +0000 | [diff] [blame] | 548 | .. function:: frozenset([iterable]) |
| 549 | :noindex: |
| 550 | |
Chris Jerdonek | df3abec | 2012-11-09 18:57:32 -0800 | [diff] [blame] | 551 | Return a new :class:`frozenset` object, optionally with elements taken from |
| 552 | *iterable*. ``frozenset`` is a built-in class. See :class:`frozenset` and |
| 553 | :ref:`types-set` for documentation about this class. |
Georg Brandl | 116aa62 | 2007-08-15 14:28:22 +0000 | [diff] [blame] | 554 | |
Chris Jerdonek | df3abec | 2012-11-09 18:57:32 -0800 | [diff] [blame] | 555 | For other containers see the built-in :class:`set`, :class:`list`, |
| 556 | :class:`tuple`, and :class:`dict` classes, as well as the :mod:`collections` |
| 557 | module. |
Georg Brandl | 116aa62 | 2007-08-15 14:28:22 +0000 | [diff] [blame] | 558 | |
Georg Brandl | 116aa62 | 2007-08-15 14:28:22 +0000 | [diff] [blame] | 559 | |
| 560 | .. function:: getattr(object, name[, default]) |
| 561 | |
Georg Brandl | 8e4ddcf | 2010-10-16 18:51:05 +0000 | [diff] [blame] | 562 | Return the value of the named attribute of *object*. *name* must be a string. |
Georg Brandl | 116aa62 | 2007-08-15 14:28:22 +0000 | [diff] [blame] | 563 | If the string is the name of one of the object's attributes, the result is the |
| 564 | value of that attribute. For example, ``getattr(x, 'foobar')`` is equivalent to |
| 565 | ``x.foobar``. If the named attribute does not exist, *default* is returned if |
| 566 | provided, otherwise :exc:`AttributeError` is raised. |
| 567 | |
| 568 | |
| 569 | .. function:: globals() |
| 570 | |
| 571 | Return a dictionary representing the current global symbol table. This is always |
| 572 | the dictionary of the current module (inside a function or method, this is the |
| 573 | module where it is defined, not the module from which it is called). |
| 574 | |
| 575 | |
| 576 | .. function:: hasattr(object, name) |
| 577 | |
Benjamin Peterson | 1768999 | 2010-08-24 03:26:23 +0000 | [diff] [blame] | 578 | The arguments are an object and a string. The result is ``True`` if the |
| 579 | string is the name of one of the object's attributes, ``False`` if not. (This |
| 580 | is implemented by calling ``getattr(object, name)`` and seeing whether it |
| 581 | raises an :exc:`AttributeError` or not.) |
Georg Brandl | 116aa62 | 2007-08-15 14:28:22 +0000 | [diff] [blame] | 582 | |
| 583 | |
| 584 | .. function:: hash(object) |
| 585 | |
| 586 | Return the hash value of the object (if it has one). Hash values are integers. |
| 587 | They are used to quickly compare dictionary keys during a dictionary lookup. |
| 588 | Numeric values that compare equal have the same hash value (even if they are of |
| 589 | different types, as is the case for 1 and 1.0). |
| 590 | |
| 591 | |
| 592 | .. function:: help([object]) |
| 593 | |
| 594 | Invoke the built-in help system. (This function is intended for interactive |
| 595 | use.) If no argument is given, the interactive help system starts on the |
| 596 | interpreter console. If the argument is a string, then the string is looked up |
| 597 | as the name of a module, function, class, method, keyword, or documentation |
| 598 | topic, and a help page is printed on the console. If the argument is any other |
| 599 | kind of object, a help page on the object is generated. |
| 600 | |
Christian Heimes | 9bd667a | 2008-01-20 15:14:11 +0000 | [diff] [blame] | 601 | This function is added to the built-in namespace by the :mod:`site` module. |
| 602 | |
Georg Brandl | 116aa62 | 2007-08-15 14:28:22 +0000 | [diff] [blame] | 603 | |
| 604 | .. function:: hex(x) |
| 605 | |
| 606 | Convert an integer number to a hexadecimal string. The result is a valid Python |
| 607 | expression. If *x* is not a Python :class:`int` object, it has to define an |
| 608 | :meth:`__index__` method that returns an integer. |
| 609 | |
Mark Dickinson | 36cea39 | 2009-10-03 10:18:40 +0000 | [diff] [blame] | 610 | .. note:: |
| 611 | |
| 612 | To obtain a hexadecimal string representation for a float, use the |
| 613 | :meth:`float.hex` method. |
| 614 | |
Georg Brandl | 116aa62 | 2007-08-15 14:28:22 +0000 | [diff] [blame] | 615 | |
| 616 | .. function:: id(object) |
| 617 | |
Georg Brandl | ba956ae | 2007-11-29 17:24:34 +0000 | [diff] [blame] | 618 | Return the "identity" of an object. This is an integer which |
Georg Brandl | 116aa62 | 2007-08-15 14:28:22 +0000 | [diff] [blame] | 619 | is guaranteed to be unique and constant for this object during its lifetime. |
Georg Brandl | 495f7b5 | 2009-10-27 15:28:25 +0000 | [diff] [blame] | 620 | Two objects with non-overlapping lifetimes may have the same :func:`id` |
| 621 | value. |
| 622 | |
Éric Araujo | f33de71 | 2011-05-27 04:42:47 +0200 | [diff] [blame] | 623 | .. impl-detail:: This is the address of the object in memory. |
Georg Brandl | 116aa62 | 2007-08-15 14:28:22 +0000 | [diff] [blame] | 624 | |
| 625 | |
Georg Brandl | c090298 | 2007-09-12 21:29:27 +0000 | [diff] [blame] | 626 | .. function:: input([prompt]) |
| 627 | |
| 628 | If the *prompt* argument is present, it is written to standard output without |
| 629 | a trailing newline. The function then reads a line from input, converts it |
| 630 | to a string (stripping a trailing newline), and returns that. When EOF is |
| 631 | read, :exc:`EOFError` is raised. Example:: |
| 632 | |
Andrew Svetlov | 439e17f | 2012-08-12 15:16:42 +0300 | [diff] [blame] | 633 | >>> s = input('--> ') # doctest: +SKIP |
Georg Brandl | c090298 | 2007-09-12 21:29:27 +0000 | [diff] [blame] | 634 | --> Monty Python's Flying Circus |
Andrew Svetlov | 439e17f | 2012-08-12 15:16:42 +0300 | [diff] [blame] | 635 | >>> s # doctest: +SKIP |
Georg Brandl | c090298 | 2007-09-12 21:29:27 +0000 | [diff] [blame] | 636 | "Monty Python's Flying Circus" |
| 637 | |
Georg Brandl | 7b46942 | 2007-09-12 21:32:27 +0000 | [diff] [blame] | 638 | If the :mod:`readline` module was loaded, then :func:`input` will use it |
Georg Brandl | c090298 | 2007-09-12 21:29:27 +0000 | [diff] [blame] | 639 | to provide elaborate line editing and history features. |
| 640 | |
| 641 | |
Chris Jerdonek | 57491e0 | 2012-09-28 00:10:44 -0700 | [diff] [blame] | 642 | .. function:: int(x=0) |
| 643 | int(x, base=10) |
Georg Brandl | 116aa62 | 2007-08-15 14:28:22 +0000 | [diff] [blame] | 644 | |
Chris Jerdonek | 57491e0 | 2012-09-28 00:10:44 -0700 | [diff] [blame] | 645 | Convert a number or string *x* to an integer, or return ``0`` if no |
| 646 | arguments are given. If *x* is a number, return :meth:`x.__int__() |
| 647 | <object.__int__>`. For floating point numbers, this truncates towards zero. |
| 648 | |
| 649 | If *x* is not a number or if *base* is given, then *x* must be a string, |
| 650 | :class:`bytes`, or :class:`bytearray` instance representing an :ref:`integer |
| 651 | literal <integers>` in radix *base*. Optionally, the literal can be |
| 652 | preceded by ``+`` or ``-`` (with no space in between) and surrounded by |
| 653 | whitespace. A base-n literal consists of the digits 0 to n-1, with ``a`` |
| 654 | to ``z`` (or ``A`` to ``Z``) having |
Georg Brandl | 1b5ab45 | 2009-08-13 07:56:35 +0000 | [diff] [blame] | 655 | values 10 to 35. The default *base* is 10. The allowed values are 0 and 2-36. |
Georg Brandl | 225d3c8 | 2008-04-09 18:45:14 +0000 | [diff] [blame] | 656 | Base-2, -8, and -16 literals can be optionally prefixed with ``0b``/``0B``, |
Georg Brandl | 1b5ab45 | 2009-08-13 07:56:35 +0000 | [diff] [blame] | 657 | ``0o``/``0O``, or ``0x``/``0X``, as with integer literals in code. Base 0 |
| 658 | means to interpret exactly as a code literal, so that the actual base is 2, |
Georg Brandl | 225d3c8 | 2008-04-09 18:45:14 +0000 | [diff] [blame] | 659 | 8, 10, or 16, and so that ``int('010', 0)`` is not legal, while |
| 660 | ``int('010')`` is, as well as ``int('010', 8)``. |
Georg Brandl | 116aa62 | 2007-08-15 14:28:22 +0000 | [diff] [blame] | 661 | |
| 662 | The integer type is described in :ref:`typesnumeric`. |
| 663 | |
| 664 | |
| 665 | .. function:: isinstance(object, classinfo) |
| 666 | |
Georg Brandl | 85eb8c1 | 2007-08-31 16:33:38 +0000 | [diff] [blame] | 667 | Return true if the *object* argument is an instance of the *classinfo* |
Éric Araujo | e8b7eb0 | 2011-08-19 02:17:03 +0200 | [diff] [blame] | 668 | argument, or of a (direct, indirect or :term:`virtual <abstract base |
| 669 | class>`) subclass thereof. If *object* is not |
Georg Brandl | 85eb8c1 | 2007-08-31 16:33:38 +0000 | [diff] [blame] | 670 | an object of the given type, the function always returns false. If |
| 671 | *classinfo* is not a class (type object), it may be a tuple of type objects, |
| 672 | or may recursively contain other such tuples (other sequence types are not |
| 673 | accepted). If *classinfo* is not a type or tuple of types and such tuples, |
| 674 | a :exc:`TypeError` exception is raised. |
Georg Brandl | 116aa62 | 2007-08-15 14:28:22 +0000 | [diff] [blame] | 675 | |
Georg Brandl | 116aa62 | 2007-08-15 14:28:22 +0000 | [diff] [blame] | 676 | |
| 677 | .. function:: issubclass(class, classinfo) |
| 678 | |
Éric Araujo | e8b7eb0 | 2011-08-19 02:17:03 +0200 | [diff] [blame] | 679 | Return true if *class* is a subclass (direct, indirect or :term:`virtual |
| 680 | <abstract base class>`) of *classinfo*. A |
Georg Brandl | 116aa62 | 2007-08-15 14:28:22 +0000 | [diff] [blame] | 681 | class is considered a subclass of itself. *classinfo* may be a tuple of class |
| 682 | objects, in which case every entry in *classinfo* will be checked. In any other |
| 683 | case, a :exc:`TypeError` exception is raised. |
| 684 | |
Georg Brandl | 116aa62 | 2007-08-15 14:28:22 +0000 | [diff] [blame] | 685 | |
Georg Brandl | 036490d | 2009-05-17 13:00:36 +0000 | [diff] [blame] | 686 | .. function:: iter(object[, sentinel]) |
Georg Brandl | 116aa62 | 2007-08-15 14:28:22 +0000 | [diff] [blame] | 687 | |
Georg Brandl | 036490d | 2009-05-17 13:00:36 +0000 | [diff] [blame] | 688 | Return an :term:`iterator` object. The first argument is interpreted very |
| 689 | differently depending on the presence of the second argument. Without a |
| 690 | second argument, *object* must be a collection object which supports the |
| 691 | iteration protocol (the :meth:`__iter__` method), or it must support the |
| 692 | sequence protocol (the :meth:`__getitem__` method with integer arguments |
| 693 | starting at ``0``). If it does not support either of those protocols, |
| 694 | :exc:`TypeError` is raised. If the second argument, *sentinel*, is given, |
| 695 | then *object* must be a callable object. The iterator created in this case |
Ezio Melotti | 7fa8222 | 2012-10-12 13:42:08 +0300 | [diff] [blame] | 696 | will call *object* with no arguments for each call to its |
| 697 | :meth:`~iterator.__next__` method; if the value returned is equal to |
| 698 | *sentinel*, :exc:`StopIteration` will be raised, otherwise the value will |
| 699 | be returned. |
Georg Brandl | 116aa62 | 2007-08-15 14:28:22 +0000 | [diff] [blame] | 700 | |
Chris Jerdonek | 006d907 | 2012-10-12 20:28:26 -0700 | [diff] [blame] | 701 | See also :ref:`typeiter`. |
| 702 | |
Benjamin Peterson | f07d002 | 2009-03-21 17:31:58 +0000 | [diff] [blame] | 703 | One useful application of the second form of :func:`iter` is to read lines of |
| 704 | a file until a certain line is reached. The following example reads a file |
Raymond Hettinger | 9028928 | 2011-06-01 16:17:23 -0700 | [diff] [blame] | 705 | until the :meth:`readline` method returns an empty string:: |
Benjamin Peterson | f07d002 | 2009-03-21 17:31:58 +0000 | [diff] [blame] | 706 | |
Raymond Hettinger | 9028928 | 2011-06-01 16:17:23 -0700 | [diff] [blame] | 707 | with open('mydata.txt') as fp: |
| 708 | for line in iter(fp.readline, ''): |
Benjamin Peterson | f07d002 | 2009-03-21 17:31:58 +0000 | [diff] [blame] | 709 | process_line(line) |
| 710 | |
Georg Brandl | 116aa62 | 2007-08-15 14:28:22 +0000 | [diff] [blame] | 711 | |
| 712 | .. function:: len(s) |
| 713 | |
| 714 | Return the length (the number of items) of an object. The argument may be a |
| 715 | sequence (string, tuple or list) or a mapping (dictionary). |
| 716 | |
| 717 | |
Nick Coghlan | 83c0ae5 | 2012-08-21 17:42:52 +1000 | [diff] [blame] | 718 | .. _func-list: |
Georg Brandl | 116aa62 | 2007-08-15 14:28:22 +0000 | [diff] [blame] | 719 | .. function:: list([iterable]) |
Nick Coghlan | 83c0ae5 | 2012-08-21 17:42:52 +1000 | [diff] [blame] | 720 | :noindex: |
Georg Brandl | 116aa62 | 2007-08-15 14:28:22 +0000 | [diff] [blame] | 721 | |
Nick Coghlan | 83c0ae5 | 2012-08-21 17:42:52 +1000 | [diff] [blame] | 722 | Rather than being a function, :class:`list` is actually a mutable |
Chris Jerdonek | 006d907 | 2012-10-12 20:28:26 -0700 | [diff] [blame] | 723 | sequence type, as documented in :ref:`typesseq-list` and :ref:`typesseq`. |
Georg Brandl | 116aa62 | 2007-08-15 14:28:22 +0000 | [diff] [blame] | 724 | |
Georg Brandl | 036490d | 2009-05-17 13:00:36 +0000 | [diff] [blame] | 725 | |
Georg Brandl | 116aa62 | 2007-08-15 14:28:22 +0000 | [diff] [blame] | 726 | .. function:: locals() |
| 727 | |
| 728 | Update and return a dictionary representing the current local symbol table. |
Benjamin Peterson | 4ac9ce4 | 2009-10-04 14:49:41 +0000 | [diff] [blame] | 729 | Free variables are returned by :func:`locals` when it is called in function |
| 730 | blocks, but not in class blocks. |
Georg Brandl | 116aa62 | 2007-08-15 14:28:22 +0000 | [diff] [blame] | 731 | |
Georg Brandl | e720c0a | 2009-04-27 16:20:50 +0000 | [diff] [blame] | 732 | .. note:: |
Georg Brandl | 036490d | 2009-05-17 13:00:36 +0000 | [diff] [blame] | 733 | The contents of this dictionary should not be modified; changes may not |
Benjamin Peterson | 4ac9ce4 | 2009-10-04 14:49:41 +0000 | [diff] [blame] | 734 | affect the values of local and free variables used by the interpreter. |
Georg Brandl | 116aa62 | 2007-08-15 14:28:22 +0000 | [diff] [blame] | 735 | |
| 736 | .. function:: map(function, iterable, ...) |
| 737 | |
Georg Brandl | 952aea2 | 2007-09-04 17:50:40 +0000 | [diff] [blame] | 738 | Return an iterator that applies *function* to every item of *iterable*, |
| 739 | yielding the results. If additional *iterable* arguments are passed, |
| 740 | *function* must take that many arguments and is applied to the items from all |
Georg Brandl | de2b00e | 2008-05-05 21:04:12 +0000 | [diff] [blame] | 741 | iterables in parallel. With multiple iterables, the iterator stops when the |
Raymond Hettinger | cdf8ba3 | 2009-02-19 04:45:07 +0000 | [diff] [blame] | 742 | shortest iterable is exhausted. For cases where the function inputs are |
| 743 | already arranged into argument tuples, see :func:`itertools.starmap`\. |
Georg Brandl | de2b00e | 2008-05-05 21:04:12 +0000 | [diff] [blame] | 744 | |
Georg Brandl | 116aa62 | 2007-08-15 14:28:22 +0000 | [diff] [blame] | 745 | |
Ezio Melotti | e0add76 | 2012-09-14 06:32:35 +0300 | [diff] [blame] | 746 | .. function:: max(iterable, *[, key]) |
| 747 | max(arg1, arg2, *args[, key]) |
Georg Brandl | 116aa62 | 2007-08-15 14:28:22 +0000 | [diff] [blame] | 748 | |
Ezio Melotti | e0add76 | 2012-09-14 06:32:35 +0300 | [diff] [blame] | 749 | Return the largest item in an iterable or the largest of two or more |
| 750 | arguments. |
| 751 | |
| 752 | If one positional argument is provided, *iterable* must be a non-empty |
| 753 | iterable (such as a non-empty string, tuple or list). The largest item |
| 754 | in the iterable is returned. If two or more positional arguments are |
| 755 | provided, the largest of the positional arguments is returned. |
Georg Brandl | 116aa62 | 2007-08-15 14:28:22 +0000 | [diff] [blame] | 756 | |
Georg Brandl | 55ac8f0 | 2007-09-01 13:51:09 +0000 | [diff] [blame] | 757 | The optional keyword-only *key* argument specifies a one-argument ordering |
| 758 | function like that used for :meth:`list.sort`. |
Georg Brandl | 116aa62 | 2007-08-15 14:28:22 +0000 | [diff] [blame] | 759 | |
Georg Brandl | 682d7e0 | 2010-10-06 10:26:05 +0000 | [diff] [blame] | 760 | If multiple items are maximal, the function returns the first one |
| 761 | encountered. This is consistent with other sort-stability preserving tools |
| 762 | such as ``sorted(iterable, key=keyfunc, reverse=True)[0]`` and |
Raymond Hettinger | 476a31e | 2010-09-14 23:13:42 +0000 | [diff] [blame] | 763 | ``heapq.nlargest(1, iterable, key=keyfunc)``. |
Georg Brandl | 116aa62 | 2007-08-15 14:28:22 +0000 | [diff] [blame] | 764 | |
Éric Araujo | 9edd9f0 | 2011-09-01 23:08:55 +0200 | [diff] [blame] | 765 | |
| 766 | .. _func-memoryview: |
Georg Brandl | 85eb8c1 | 2007-08-31 16:33:38 +0000 | [diff] [blame] | 767 | .. function:: memoryview(obj) |
Benjamin Peterson | 6dfcb02 | 2008-09-10 21:02:02 +0000 | [diff] [blame] | 768 | :noindex: |
Georg Brandl | 85eb8c1 | 2007-08-31 16:33:38 +0000 | [diff] [blame] | 769 | |
Benjamin Peterson | 1b25b92 | 2008-09-09 22:15:27 +0000 | [diff] [blame] | 770 | Return a "memory view" object created from the given argument. See |
| 771 | :ref:`typememoryview` for more information. |
Georg Brandl | 85eb8c1 | 2007-08-31 16:33:38 +0000 | [diff] [blame] | 772 | |
| 773 | |
Ezio Melotti | e0add76 | 2012-09-14 06:32:35 +0300 | [diff] [blame] | 774 | .. function:: min(iterable, *[, key]) |
| 775 | min(arg1, arg2, *args[, key]) |
Georg Brandl | 116aa62 | 2007-08-15 14:28:22 +0000 | [diff] [blame] | 776 | |
Ezio Melotti | e0add76 | 2012-09-14 06:32:35 +0300 | [diff] [blame] | 777 | Return the smallest item in an iterable or the smallest of two or more |
| 778 | arguments. |
| 779 | |
| 780 | If one positional argument is provided, *iterable* must be a non-empty |
| 781 | iterable (such as a non-empty string, tuple or list). The smallest item |
| 782 | in the iterable is returned. If two or more positional arguments are |
| 783 | provided, the smallest of the positional arguments is returned. |
Georg Brandl | 116aa62 | 2007-08-15 14:28:22 +0000 | [diff] [blame] | 784 | |
Georg Brandl | 55ac8f0 | 2007-09-01 13:51:09 +0000 | [diff] [blame] | 785 | The optional keyword-only *key* argument specifies a one-argument ordering |
| 786 | function like that used for :meth:`list.sort`. |
Georg Brandl | 116aa62 | 2007-08-15 14:28:22 +0000 | [diff] [blame] | 787 | |
Georg Brandl | 682d7e0 | 2010-10-06 10:26:05 +0000 | [diff] [blame] | 788 | If multiple items are minimal, the function returns the first one |
| 789 | encountered. This is consistent with other sort-stability preserving tools |
| 790 | such as ``sorted(iterable, key=keyfunc)[0]`` and ``heapq.nsmallest(1, |
| 791 | iterable, key=keyfunc)``. |
Georg Brandl | 116aa62 | 2007-08-15 14:28:22 +0000 | [diff] [blame] | 792 | |
| 793 | .. function:: next(iterator[, default]) |
| 794 | |
Ezio Melotti | 7fa8222 | 2012-10-12 13:42:08 +0300 | [diff] [blame] | 795 | Retrieve the next item from the *iterator* by calling its |
| 796 | :meth:`~iterator.__next__` method. If *default* is given, it is returned |
| 797 | if the iterator is exhausted, otherwise :exc:`StopIteration` is raised. |
Georg Brandl | 116aa62 | 2007-08-15 14:28:22 +0000 | [diff] [blame] | 798 | |
| 799 | |
| 800 | .. function:: object() |
| 801 | |
Georg Brandl | 85eb8c1 | 2007-08-31 16:33:38 +0000 | [diff] [blame] | 802 | Return a new featureless object. :class:`object` is a base for all classes. |
Georg Brandl | 55ac8f0 | 2007-09-01 13:51:09 +0000 | [diff] [blame] | 803 | It has the methods that are common to all instances of Python classes. This |
| 804 | function does not accept any arguments. |
Georg Brandl | 85eb8c1 | 2007-08-31 16:33:38 +0000 | [diff] [blame] | 805 | |
| 806 | .. note:: |
| 807 | |
| 808 | :class:`object` does *not* have a :attr:`__dict__`, so you can't assign |
| 809 | arbitrary attributes to an instance of the :class:`object` class. |
Georg Brandl | 116aa62 | 2007-08-15 14:28:22 +0000 | [diff] [blame] | 810 | |
Georg Brandl | 116aa62 | 2007-08-15 14:28:22 +0000 | [diff] [blame] | 811 | |
| 812 | .. function:: oct(x) |
| 813 | |
| 814 | Convert an integer number to an octal string. The result is a valid Python |
| 815 | expression. If *x* is not a Python :class:`int` object, it has to define an |
| 816 | :meth:`__index__` method that returns an integer. |
| 817 | |
Georg Brandl | 116aa62 | 2007-08-15 14:28:22 +0000 | [diff] [blame] | 818 | |
R David Murray | 9f0c940 | 2012-08-17 20:33:54 -0400 | [diff] [blame] | 819 | .. index:: |
| 820 | single: file object; open() built-in function |
| 821 | |
Ross Lagerwall | 59142db | 2011-10-31 20:34:46 +0200 | [diff] [blame] | 822 | .. function:: open(file, mode='r', buffering=-1, encoding=None, errors=None, newline=None, closefd=True, opener=None) |
Georg Brandl | 116aa62 | 2007-08-15 14:28:22 +0000 | [diff] [blame] | 823 | |
R David Murray | 9f0c940 | 2012-08-17 20:33:54 -0400 | [diff] [blame] | 824 | Open *file* and return a corresponding :term:`file object`. If the file |
R David Murray | 8eac575 | 2012-08-17 20:38:19 -0400 | [diff] [blame] | 825 | cannot be opened, an :exc:`OSError` is raised. |
Georg Brandl | 48310cd | 2009-01-03 21:18:54 +0000 | [diff] [blame] | 826 | |
Benjamin Peterson | 4e4ffb1 | 2010-08-30 12:46:09 +0000 | [diff] [blame] | 827 | *file* is either a string or bytes object giving the pathname (absolute or |
| 828 | relative to the current working directory) of the file to be opened or |
Georg Brandl | 76e5538 | 2008-10-08 16:34:57 +0000 | [diff] [blame] | 829 | an integer file descriptor of the file to be wrapped. (If a file descriptor |
| 830 | is given, it is closed when the returned I/O object is closed, unless |
| 831 | *closefd* is set to ``False``.) |
Georg Brandl | 116aa62 | 2007-08-15 14:28:22 +0000 | [diff] [blame] | 832 | |
Mark Summerfield | ecff60e | 2007-12-14 10:07:44 +0000 | [diff] [blame] | 833 | *mode* is an optional string that specifies the mode in which the file is |
Benjamin Peterson | 4e4ffb1 | 2010-08-30 12:46:09 +0000 | [diff] [blame] | 834 | opened. It defaults to ``'r'`` which means open for reading in text mode. |
| 835 | Other common values are ``'w'`` for writing (truncating the file if it |
Charles-François Natali | b93f9fa | 2012-05-20 11:41:53 +0200 | [diff] [blame] | 836 | already exists), ``'x'`` for exclusive creation and ``'a'`` for appending |
| 837 | (which on *some* Unix systems, means that *all* writes append to the end of |
| 838 | the file regardless of the current seek position). In text mode, if |
Victor Stinner | f86a5e8 | 2012-06-05 13:43:22 +0200 | [diff] [blame] | 839 | *encoding* is not specified the encoding used is platform dependent: |
| 840 | ``locale.getpreferredencoding(False)`` is called to get the current locale |
| 841 | encoding. (For reading and writing raw bytes use binary mode and leave |
| 842 | *encoding* unspecified.) The available modes are: |
Georg Brandl | 116aa62 | 2007-08-15 14:28:22 +0000 | [diff] [blame] | 843 | |
Benjamin Peterson | dd21912 | 2008-04-11 21:17:32 +0000 | [diff] [blame] | 844 | ========= =============================================================== |
| 845 | Character Meaning |
| 846 | --------- --------------------------------------------------------------- |
| 847 | ``'r'`` open for reading (default) |
Benjamin Peterson | 4e4ffb1 | 2010-08-30 12:46:09 +0000 | [diff] [blame] | 848 | ``'w'`` open for writing, truncating the file first |
Charles-François Natali | b93f9fa | 2012-05-20 11:41:53 +0200 | [diff] [blame] | 849 | ``'x'`` open for exclusive creation, failing if the file already exists |
Benjamin Peterson | dd21912 | 2008-04-11 21:17:32 +0000 | [diff] [blame] | 850 | ``'a'`` open for writing, appending to the end of the file if it exists |
Georg Brandl | 7b6ca4a | 2009-04-27 06:13:55 +0000 | [diff] [blame] | 851 | ``'b'`` binary mode |
Benjamin Peterson | 4e4ffb1 | 2010-08-30 12:46:09 +0000 | [diff] [blame] | 852 | ``'t'`` text mode (default) |
| 853 | ``'+'`` open a disk file for updating (reading and writing) |
R David Murray | 1b00f25 | 2012-08-15 10:43:58 -0400 | [diff] [blame] | 854 | ``'U'`` universal newlines mode (for backwards compatibility; should |
Benjamin Peterson | 52c3bf1 | 2009-03-23 02:44:58 +0000 | [diff] [blame] | 855 | not be used in new code) |
Benjamin Peterson | dd21912 | 2008-04-11 21:17:32 +0000 | [diff] [blame] | 856 | ========= =============================================================== |
Mark Summerfield | ecff60e | 2007-12-14 10:07:44 +0000 | [diff] [blame] | 857 | |
Benjamin Peterson | 4e4ffb1 | 2010-08-30 12:46:09 +0000 | [diff] [blame] | 858 | The default mode is ``'r'`` (open for reading text, synonym of ``'rt'``). |
Benjamin Peterson | 6b4fa77 | 2010-08-30 13:19:53 +0000 | [diff] [blame] | 859 | For binary read-write access, the mode ``'w+b'`` opens and truncates the file |
| 860 | to 0 bytes. ``'r+b'`` opens the file without truncation. |
Skip Montanaro | 1c63960 | 2007-09-23 19:49:54 +0000 | [diff] [blame] | 861 | |
Benjamin Peterson | 6b4fa77 | 2010-08-30 13:19:53 +0000 | [diff] [blame] | 862 | As mentioned in the :ref:`io-overview`, Python distinguishes between binary |
| 863 | and text I/O. Files opened in binary mode (including ``'b'`` in the *mode* |
| 864 | argument) return contents as :class:`bytes` objects without any decoding. In |
| 865 | text mode (the default, or when ``'t'`` is included in the *mode* argument), |
| 866 | the contents of the file are returned as :class:`str`, the bytes having been |
| 867 | first decoded using a platform-dependent encoding or using the specified |
| 868 | *encoding* if given. |
Mark Summerfield | ecff60e | 2007-12-14 10:07:44 +0000 | [diff] [blame] | 869 | |
Benjamin Peterson | 4e4ffb1 | 2010-08-30 12:46:09 +0000 | [diff] [blame] | 870 | .. note:: |
Benjamin Peterson | 4e4ffb1 | 2010-08-30 12:46:09 +0000 | [diff] [blame] | 871 | |
Benjamin Peterson | 6b4fa77 | 2010-08-30 13:19:53 +0000 | [diff] [blame] | 872 | Python doesn't depend on the underlying operating system's notion of text |
Ezio Melotti | e130a52 | 2011-10-19 10:58:56 +0300 | [diff] [blame] | 873 | files; all the processing is done by Python itself, and is therefore |
Benjamin Peterson | 6b4fa77 | 2010-08-30 13:19:53 +0000 | [diff] [blame] | 874 | platform-independent. |
Benjamin Peterson | 4e4ffb1 | 2010-08-30 12:46:09 +0000 | [diff] [blame] | 875 | |
Benjamin Peterson | 6b4fa77 | 2010-08-30 13:19:53 +0000 | [diff] [blame] | 876 | *buffering* is an optional integer used to set the buffering policy. Pass 0 |
| 877 | to switch buffering off (only allowed in binary mode), 1 to select line |
| 878 | buffering (only usable in text mode), and an integer > 1 to indicate the size |
| 879 | of a fixed-size chunk buffer. When no *buffering* argument is given, the |
| 880 | default buffering policy works as follows: |
Benjamin Peterson | 4e4ffb1 | 2010-08-30 12:46:09 +0000 | [diff] [blame] | 881 | |
Benjamin Peterson | 6b4fa77 | 2010-08-30 13:19:53 +0000 | [diff] [blame] | 882 | * Binary files are buffered in fixed-size chunks; the size of the buffer is |
| 883 | chosen using a heuristic trying to determine the underlying device's "block |
| 884 | size" and falling back on :attr:`io.DEFAULT_BUFFER_SIZE`. On many systems, |
| 885 | the buffer will typically be 4096 or 8192 bytes long. |
| 886 | |
| 887 | * "Interactive" text files (files for which :meth:`isatty` returns True) use |
| 888 | line buffering. Other text files use the policy described above for binary |
| 889 | files. |
Georg Brandl | 48310cd | 2009-01-03 21:18:54 +0000 | [diff] [blame] | 890 | |
Benjamin Peterson | dd21912 | 2008-04-11 21:17:32 +0000 | [diff] [blame] | 891 | *encoding* is the name of the encoding used to decode or encode the file. |
| 892 | This should only be used in text mode. The default encoding is platform |
Benjamin Peterson | 52c3bf1 | 2009-03-23 02:44:58 +0000 | [diff] [blame] | 893 | dependent (whatever :func:`locale.getpreferredencoding` returns), but any |
| 894 | encoding supported by Python can be used. See the :mod:`codecs` module for |
| 895 | the list of supported encodings. |
Mark Summerfield | ecff60e | 2007-12-14 10:07:44 +0000 | [diff] [blame] | 896 | |
Benjamin Peterson | 52c3bf1 | 2009-03-23 02:44:58 +0000 | [diff] [blame] | 897 | *errors* is an optional string that specifies how encoding and decoding |
| 898 | errors are to be handled--this cannot be used in binary mode. Pass |
| 899 | ``'strict'`` to raise a :exc:`ValueError` exception if there is an encoding |
| 900 | error (the default of ``None`` has the same effect), or pass ``'ignore'`` to |
| 901 | ignore errors. (Note that ignoring encoding errors can lead to data loss.) |
| 902 | ``'replace'`` causes a replacement marker (such as ``'?'``) to be inserted |
| 903 | where there is malformed data. When writing, ``'xmlcharrefreplace'`` |
| 904 | (replace with the appropriate XML character reference) or |
| 905 | ``'backslashreplace'`` (replace with backslashed escape sequences) can be |
| 906 | used. Any other error handling name that has been registered with |
| 907 | :func:`codecs.register_error` is also valid. |
Mark Summerfield | ecff60e | 2007-12-14 10:07:44 +0000 | [diff] [blame] | 908 | |
R David Murray | 1b00f25 | 2012-08-15 10:43:58 -0400 | [diff] [blame] | 909 | .. index:: |
| 910 | single: universal newlines; open() built-in function |
| 911 | |
| 912 | *newline* controls how :term:`universal newlines` mode works (it only |
R David Murray | ee0a945 | 2012-08-15 11:05:36 -0400 | [diff] [blame] | 913 | applies to text mode). It can be ``None``, ``''``, ``'\n'``, ``'\r'``, and |
| 914 | ``'\r\n'``. It works as follows: |
Mark Summerfield | ecff60e | 2007-12-14 10:07:44 +0000 | [diff] [blame] | 915 | |
Georg Brandl | 296d1be | 2012-08-14 09:39:07 +0200 | [diff] [blame] | 916 | * When reading input from the stream, if *newline* is ``None``, universal |
| 917 | newlines mode is enabled. Lines in the input can end in ``'\n'``, |
| 918 | ``'\r'``, or ``'\r\n'``, and these are translated into ``'\n'`` before |
R David Murray | 1b00f25 | 2012-08-15 10:43:58 -0400 | [diff] [blame] | 919 | being returned to the caller. If it is ``''``, universal newlines mode is |
Georg Brandl | 296d1be | 2012-08-14 09:39:07 +0200 | [diff] [blame] | 920 | enabled, but line endings are returned to the caller untranslated. If it |
| 921 | has any of the other legal values, input lines are only terminated by the |
| 922 | given string, and the line ending is returned to the caller untranslated. |
Benjamin Peterson | dd21912 | 2008-04-11 21:17:32 +0000 | [diff] [blame] | 923 | |
Georg Brandl | 296d1be | 2012-08-14 09:39:07 +0200 | [diff] [blame] | 924 | * When writing output to the stream, if *newline* is ``None``, any ``'\n'`` |
| 925 | characters written are translated to the system default line separator, |
| 926 | :data:`os.linesep`. If *newline* is ``''`` or ``'\n'``, no translation |
| 927 | takes place. If *newline* is any of the other legal values, any ``'\n'`` |
| 928 | characters written are translated to the given string. |
Benjamin Peterson | dd21912 | 2008-04-11 21:17:32 +0000 | [diff] [blame] | 929 | |
Benjamin Peterson | 8cad9c7 | 2009-03-23 02:38:01 +0000 | [diff] [blame] | 930 | If *closefd* is ``False`` and a file descriptor rather than a filename was |
| 931 | given, the underlying file descriptor will be kept open when the file is |
| 932 | closed. If a filename is given *closefd* has no effect and must be ``True`` |
| 933 | (the default). |
| 934 | |
Ross Lagerwall | 59142db | 2011-10-31 20:34:46 +0200 | [diff] [blame] | 935 | A custom opener can be used by passing a callable as *opener*. The underlying |
| 936 | file descriptor for the file object is then obtained by calling *opener* with |
| 937 | (*file*, *flags*). *opener* must return an open file descriptor (passing |
| 938 | :mod:`os.open` as *opener* results in functionality similar to passing |
| 939 | ``None``). |
| 940 | |
Éric Araujo | 5bd9270 | 2012-11-22 00:13:49 -0500 | [diff] [blame] | 941 | The following example uses the :ref:`dir_fd <dir_fd>` parameter of the |
Éric Araujo | 8f423c9 | 2012-11-03 17:06:52 -0400 | [diff] [blame] | 942 | :func:`os.open` function to open a file relative to a given directory:: |
| 943 | |
| 944 | >>> import os |
Éric Araujo | 5bd9270 | 2012-11-22 00:13:49 -0500 | [diff] [blame] | 945 | >>> dir_fd = os.open('somedir', os.O_RDONLY) |
| 946 | >>> def opener(path, flags): |
| 947 | ... return os.open(path, flags, dir_fd=dir_fd) |
Éric Araujo | 8f423c9 | 2012-11-03 17:06:52 -0400 | [diff] [blame] | 948 | ... |
Éric Araujo | 8f423c9 | 2012-11-03 17:06:52 -0400 | [diff] [blame] | 949 | >>> with open('spamspam.txt', 'w', opener=opener) as f: |
| 950 | ... print('This will be written to somedir/spamspam.txt', file=f) |
| 951 | ... |
Éric Araujo | 309b043 | 2012-11-03 17:39:45 -0400 | [diff] [blame] | 952 | >>> os.close(dir_fd) # don't leak a file descriptor |
Éric Araujo | 8f423c9 | 2012-11-03 17:06:52 -0400 | [diff] [blame] | 953 | |
Ross Lagerwall | 59142db | 2011-10-31 20:34:46 +0200 | [diff] [blame] | 954 | .. versionchanged:: 3.3 |
| 955 | The *opener* parameter was added. |
Charles-François Natali | b93f9fa | 2012-05-20 11:41:53 +0200 | [diff] [blame] | 956 | The ``'x'`` mode was added. |
Ross Lagerwall | 59142db | 2011-10-31 20:34:46 +0200 | [diff] [blame] | 957 | |
R David Murray | 9f0c940 | 2012-08-17 20:33:54 -0400 | [diff] [blame] | 958 | The type of :term:`file object` returned by the :func:`open` function |
R David Murray | 433ef3b | 2012-08-17 20:39:21 -0400 | [diff] [blame] | 959 | depends on the mode. When :func:`open` is used to open a file in a text |
| 960 | mode (``'w'``, ``'r'``, ``'wt'``, ``'rt'``, etc.), it returns a subclass of |
Benjamin Peterson | 6b4fa77 | 2010-08-30 13:19:53 +0000 | [diff] [blame] | 961 | :class:`io.TextIOBase` (specifically :class:`io.TextIOWrapper`). When used |
| 962 | to open a file in a binary mode with buffering, the returned class is a |
| 963 | subclass of :class:`io.BufferedIOBase`. The exact class varies: in read |
| 964 | binary mode, it returns a :class:`io.BufferedReader`; in write binary and |
| 965 | append binary modes, it returns a :class:`io.BufferedWriter`, and in |
| 966 | read/write mode, it returns a :class:`io.BufferedRandom`. When buffering is |
| 967 | disabled, the raw stream, a subclass of :class:`io.RawIOBase`, |
| 968 | :class:`io.FileIO`, is returned. |
Georg Brandl | 116aa62 | 2007-08-15 14:28:22 +0000 | [diff] [blame] | 969 | |
| 970 | .. index:: |
| 971 | single: line-buffered I/O |
| 972 | single: unbuffered I/O |
| 973 | single: buffer size, I/O |
| 974 | single: I/O control; buffering |
Skip Montanaro | 4d8c193 | 2007-09-23 21:13:45 +0000 | [diff] [blame] | 975 | single: binary mode |
| 976 | single: text mode |
| 977 | module: sys |
Georg Brandl | 116aa62 | 2007-08-15 14:28:22 +0000 | [diff] [blame] | 978 | |
Benjamin Peterson | dd21912 | 2008-04-11 21:17:32 +0000 | [diff] [blame] | 979 | See also the file handling modules, such as, :mod:`fileinput`, :mod:`io` |
Benjamin Peterson | 8cad9c7 | 2009-03-23 02:38:01 +0000 | [diff] [blame] | 980 | (where :func:`open` is declared), :mod:`os`, :mod:`os.path`, :mod:`tempfile`, |
| 981 | and :mod:`shutil`. |
Georg Brandl | 116aa62 | 2007-08-15 14:28:22 +0000 | [diff] [blame] | 982 | |
Antoine Pitrou | 62ab10a0 | 2011-10-12 20:10:51 +0200 | [diff] [blame] | 983 | .. versionchanged:: 3.3 |
| 984 | :exc:`IOError` used to be raised, it is now an alias of :exc:`OSError`. |
Charles-François Natali | b93f9fa | 2012-05-20 11:41:53 +0200 | [diff] [blame] | 985 | :exc:`FileExistsError` is now raised if the file opened in exclusive |
| 986 | creation mode (``'x'``) already exists. |
Antoine Pitrou | 62ab10a0 | 2011-10-12 20:10:51 +0200 | [diff] [blame] | 987 | |
Georg Brandl | f694518 | 2008-02-01 11:56:49 +0000 | [diff] [blame] | 988 | |
| 989 | .. XXX works for bytes too, but should it? |
Georg Brandl | 116aa62 | 2007-08-15 14:28:22 +0000 | [diff] [blame] | 990 | .. function:: ord(c) |
| 991 | |
Ezio Melotti | c99c858 | 2011-10-25 09:32:34 +0300 | [diff] [blame] | 992 | Given a string representing one Unicode character, return an integer |
Alexander Belopolsky | 5d4dd3e | 2010-11-18 18:50:13 +0000 | [diff] [blame] | 993 | representing the Unicode code |
| 994 | point of that character. For example, ``ord('a')`` returns the integer ``97`` |
Georg Brandl | f694518 | 2008-02-01 11:56:49 +0000 | [diff] [blame] | 995 | and ``ord('\u2020')`` returns ``8224``. This is the inverse of :func:`chr`. |
| 996 | |
Georg Brandl | 116aa62 | 2007-08-15 14:28:22 +0000 | [diff] [blame] | 997 | |
| 998 | .. function:: pow(x, y[, z]) |
| 999 | |
| 1000 | Return *x* to the power *y*; if *z* is present, return *x* to the power *y*, |
| 1001 | modulo *z* (computed more efficiently than ``pow(x, y) % z``). The two-argument |
| 1002 | form ``pow(x, y)`` is equivalent to using the power operator: ``x**y``. |
| 1003 | |
Georg Brandl | e06de8b | 2008-05-05 21:42:51 +0000 | [diff] [blame] | 1004 | The arguments must have numeric types. With mixed operand types, the |
| 1005 | coercion rules for binary arithmetic operators apply. For :class:`int` |
| 1006 | operands, the result has the same type as the operands (after coercion) |
| 1007 | unless the second argument is negative; in that case, all arguments are |
| 1008 | converted to float and a float result is delivered. For example, ``10**2`` |
| 1009 | returns ``100``, but ``10**-2`` returns ``0.01``. If the second argument is |
| 1010 | negative, the third argument must be omitted. If *z* is present, *x* and *y* |
| 1011 | must be of integer types, and *y* must be non-negative. |
Georg Brandl | 116aa62 | 2007-08-15 14:28:22 +0000 | [diff] [blame] | 1012 | |
| 1013 | |
Ezio Melotti | 8429b67 | 2012-09-14 06:35:09 +0300 | [diff] [blame] | 1014 | .. function:: print(*objects, sep=' ', end='\\n', file=sys.stdout, flush=False) |
Georg Brandl | f694518 | 2008-02-01 11:56:49 +0000 | [diff] [blame] | 1015 | |
Ezio Melotti | e0add76 | 2012-09-14 06:32:35 +0300 | [diff] [blame] | 1016 | Print *objects* to the stream *file*, separated by *sep* and followed by |
Georg Brandl | f694518 | 2008-02-01 11:56:49 +0000 | [diff] [blame] | 1017 | *end*. *sep*, *end* and *file*, if present, must be given as keyword |
| 1018 | arguments. |
| 1019 | |
| 1020 | All non-keyword arguments are converted to strings like :func:`str` does and |
| 1021 | written to the stream, separated by *sep* and followed by *end*. Both *sep* |
| 1022 | and *end* must be strings; they can also be ``None``, which means to use the |
Ezio Melotti | e0add76 | 2012-09-14 06:32:35 +0300 | [diff] [blame] | 1023 | default values. If no *objects* are given, :func:`print` will just write |
Georg Brandl | f694518 | 2008-02-01 11:56:49 +0000 | [diff] [blame] | 1024 | *end*. |
| 1025 | |
| 1026 | The *file* argument must be an object with a ``write(string)`` method; if it |
Georg Brandl | bc3b682 | 2012-01-13 19:41:25 +0100 | [diff] [blame] | 1027 | is not present or ``None``, :data:`sys.stdout` will be used. Whether output |
| 1028 | is buffered is usually determined by *file*, but if the *flush* keyword |
| 1029 | argument is true, the stream is forcibly flushed. |
| 1030 | |
| 1031 | .. versionchanged:: 3.3 |
| 1032 | Added the *flush* keyword argument. |
Georg Brandl | f694518 | 2008-02-01 11:56:49 +0000 | [diff] [blame] | 1033 | |
| 1034 | |
Georg Brandl | 036490d | 2009-05-17 13:00:36 +0000 | [diff] [blame] | 1035 | .. function:: property(fget=None, fset=None, fdel=None, doc=None) |
Georg Brandl | 116aa62 | 2007-08-15 14:28:22 +0000 | [diff] [blame] | 1036 | |
Georg Brandl | 85eb8c1 | 2007-08-31 16:33:38 +0000 | [diff] [blame] | 1037 | Return a property attribute. |
Georg Brandl | 116aa62 | 2007-08-15 14:28:22 +0000 | [diff] [blame] | 1038 | |
| 1039 | *fget* is a function for getting an attribute value, likewise *fset* is a |
| 1040 | function for setting, and *fdel* a function for del'ing, an attribute. Typical |
Georg Brandl | 7528b9b | 2010-08-02 19:23:34 +0000 | [diff] [blame] | 1041 | use is to define a managed attribute ``x``:: |
Georg Brandl | 116aa62 | 2007-08-15 14:28:22 +0000 | [diff] [blame] | 1042 | |
Éric Araujo | 28053fb | 2010-11-22 03:09:19 +0000 | [diff] [blame] | 1043 | class C: |
Alexandre Vassalotti | 5f8ced2 | 2008-05-16 00:03:33 +0000 | [diff] [blame] | 1044 | def __init__(self): |
| 1045 | self._x = None |
| 1046 | |
| 1047 | def getx(self): |
| 1048 | return self._x |
| 1049 | def setx(self, value): |
| 1050 | self._x = value |
| 1051 | def delx(self): |
| 1052 | del self._x |
Georg Brandl | 116aa62 | 2007-08-15 14:28:22 +0000 | [diff] [blame] | 1053 | x = property(getx, setx, delx, "I'm the 'x' property.") |
| 1054 | |
Georg Brandl | 7528b9b | 2010-08-02 19:23:34 +0000 | [diff] [blame] | 1055 | If then *c* is an instance of *C*, ``c.x`` will invoke the getter, |
| 1056 | ``c.x = value`` will invoke the setter and ``del c.x`` the deleter. |
| 1057 | |
Georg Brandl | 116aa62 | 2007-08-15 14:28:22 +0000 | [diff] [blame] | 1058 | If given, *doc* will be the docstring of the property attribute. Otherwise, the |
| 1059 | property will copy *fget*'s docstring (if it exists). This makes it possible to |
Christian Heimes | d8654cf | 2007-12-02 15:22:16 +0000 | [diff] [blame] | 1060 | create read-only properties easily using :func:`property` as a :term:`decorator`:: |
Georg Brandl | 116aa62 | 2007-08-15 14:28:22 +0000 | [diff] [blame] | 1061 | |
Éric Araujo | 28053fb | 2010-11-22 03:09:19 +0000 | [diff] [blame] | 1062 | class Parrot: |
Georg Brandl | 116aa62 | 2007-08-15 14:28:22 +0000 | [diff] [blame] | 1063 | def __init__(self): |
| 1064 | self._voltage = 100000 |
| 1065 | |
| 1066 | @property |
| 1067 | def voltage(self): |
| 1068 | """Get the current voltage.""" |
| 1069 | return self._voltage |
| 1070 | |
Alexandre Vassalotti | 5f8ced2 | 2008-05-16 00:03:33 +0000 | [diff] [blame] | 1071 | turns the :meth:`voltage` method into a "getter" for a read-only attribute |
| 1072 | with the same name. |
| 1073 | |
| 1074 | A property object has :attr:`getter`, :attr:`setter`, and :attr:`deleter` |
| 1075 | methods usable as decorators that create a copy of the property with the |
| 1076 | corresponding accessor function set to the decorated function. This is |
| 1077 | best explained with an example:: |
| 1078 | |
Éric Araujo | 28053fb | 2010-11-22 03:09:19 +0000 | [diff] [blame] | 1079 | class C: |
Benjamin Peterson | 206e307 | 2008-10-19 14:07:49 +0000 | [diff] [blame] | 1080 | def __init__(self): |
| 1081 | self._x = None |
Alexandre Vassalotti | 5f8ced2 | 2008-05-16 00:03:33 +0000 | [diff] [blame] | 1082 | |
| 1083 | @property |
| 1084 | def x(self): |
| 1085 | """I'm the 'x' property.""" |
| 1086 | return self._x |
| 1087 | |
| 1088 | @x.setter |
| 1089 | def x(self, value): |
| 1090 | self._x = value |
| 1091 | |
| 1092 | @x.deleter |
| 1093 | def x(self): |
| 1094 | del self._x |
| 1095 | |
| 1096 | This code is exactly equivalent to the first example. Be sure to give the |
| 1097 | additional functions the same name as the original property (``x`` in this |
| 1098 | case.) |
| 1099 | |
| 1100 | The returned property also has the attributes ``fget``, ``fset``, and |
| 1101 | ``fdel`` corresponding to the constructor arguments. |
Georg Brandl | 116aa62 | 2007-08-15 14:28:22 +0000 | [diff] [blame] | 1102 | |
Georg Brandl | 116aa62 | 2007-08-15 14:28:22 +0000 | [diff] [blame] | 1103 | |
Nick Coghlan | 83c0ae5 | 2012-08-21 17:42:52 +1000 | [diff] [blame] | 1104 | .. _func-range: |
Ezio Melotti | e0add76 | 2012-09-14 06:32:35 +0300 | [diff] [blame] | 1105 | .. function:: range(stop) |
| 1106 | range(start, stop[, step]) |
Nick Coghlan | 83c0ae5 | 2012-08-21 17:42:52 +1000 | [diff] [blame] | 1107 | :noindex: |
Georg Brandl | 116aa62 | 2007-08-15 14:28:22 +0000 | [diff] [blame] | 1108 | |
Nick Coghlan | 83c0ae5 | 2012-08-21 17:42:52 +1000 | [diff] [blame] | 1109 | Rather than being a function, :class:`range` is actually an immutable |
Chris Jerdonek | 006d907 | 2012-10-12 20:28:26 -0700 | [diff] [blame] | 1110 | sequence type, as documented in :ref:`typesseq-range` and :ref:`typesseq`. |
Benjamin Peterson | 878ce38 | 2011-11-05 15:17:52 -0400 | [diff] [blame] | 1111 | |
Georg Brandl | 116aa62 | 2007-08-15 14:28:22 +0000 | [diff] [blame] | 1112 | |
| 1113 | .. function:: repr(object) |
| 1114 | |
Georg Brandl | 68ee3a5 | 2008-03-25 07:21:32 +0000 | [diff] [blame] | 1115 | Return a string containing a printable representation of an object. For many |
| 1116 | types, this function makes an attempt to return a string that would yield an |
| 1117 | object with the same value when passed to :func:`eval`, otherwise the |
| 1118 | representation is a string enclosed in angle brackets that contains the name |
| 1119 | of the type of the object together with additional information often |
| 1120 | including the name and address of the object. A class can control what this |
| 1121 | function returns for its instances by defining a :meth:`__repr__` method. |
Georg Brandl | 116aa62 | 2007-08-15 14:28:22 +0000 | [diff] [blame] | 1122 | |
| 1123 | |
| 1124 | .. function:: reversed(seq) |
| 1125 | |
Christian Heimes | 7f04431 | 2008-01-06 17:05:40 +0000 | [diff] [blame] | 1126 | Return a reverse :term:`iterator`. *seq* must be an object which has |
| 1127 | a :meth:`__reversed__` method or supports the sequence protocol (the |
| 1128 | :meth:`__len__` method and the :meth:`__getitem__` method with integer |
| 1129 | arguments starting at ``0``). |
Georg Brandl | 116aa62 | 2007-08-15 14:28:22 +0000 | [diff] [blame] | 1130 | |
Georg Brandl | 116aa62 | 2007-08-15 14:28:22 +0000 | [diff] [blame] | 1131 | |
Mark Dickinson | 4e12ad1 | 2012-09-20 20:51:14 +0100 | [diff] [blame] | 1132 | .. function:: round(number[, ndigits]) |
Georg Brandl | 116aa62 | 2007-08-15 14:28:22 +0000 | [diff] [blame] | 1133 | |
Mark Dickinson | 4e12ad1 | 2012-09-20 20:51:14 +0100 | [diff] [blame] | 1134 | Return the floating point value *number* rounded to *ndigits* digits after |
| 1135 | the decimal point. If *ndigits* is omitted, it defaults to zero. Delegates |
| 1136 | to ``number.__round__(ndigits)``. |
Georg Brandl | 809ddaa | 2008-07-01 20:39:59 +0000 | [diff] [blame] | 1137 | |
| 1138 | For the built-in types supporting :func:`round`, values are rounded to the |
Mark Dickinson | 4e12ad1 | 2012-09-20 20:51:14 +0100 | [diff] [blame] | 1139 | closest multiple of 10 to the power minus *ndigits*; if two multiples are |
| 1140 | equally close, rounding is done toward the even choice (so, for example, |
| 1141 | both ``round(0.5)`` and ``round(-0.5)`` are ``0``, and ``round(1.5)`` is |
| 1142 | ``2``). The return value is an integer if called with one argument, |
| 1143 | otherwise of the same type as *number*. |
Christian Heimes | 072c0f1 | 2008-01-03 23:01:04 +0000 | [diff] [blame] | 1144 | |
Mark Dickinson | c4fbcdc | 2010-07-30 13:13:02 +0000 | [diff] [blame] | 1145 | .. note:: |
| 1146 | |
| 1147 | The behavior of :func:`round` for floats can be surprising: for example, |
| 1148 | ``round(2.675, 2)`` gives ``2.67`` instead of the expected ``2.68``. |
| 1149 | This is not a bug: it's a result of the fact that most decimal fractions |
| 1150 | can't be represented exactly as a float. See :ref:`tut-fp-issues` for |
| 1151 | more information. |
Georg Brandl | 116aa62 | 2007-08-15 14:28:22 +0000 | [diff] [blame] | 1152 | |
Éric Araujo | 9edd9f0 | 2011-09-01 23:08:55 +0200 | [diff] [blame] | 1153 | |
| 1154 | .. _func-set: |
Georg Brandl | 116aa62 | 2007-08-15 14:28:22 +0000 | [diff] [blame] | 1155 | .. function:: set([iterable]) |
| 1156 | :noindex: |
| 1157 | |
Chris Jerdonek | df3abec | 2012-11-09 18:57:32 -0800 | [diff] [blame] | 1158 | Return a new :class:`set` object, optionally with elements taken from |
| 1159 | *iterable*. ``set`` is a built-in class. See :class:`set` and |
| 1160 | :ref:`types-set` for documentation about this class. |
| 1161 | |
| 1162 | For other containers see the built-in :class:`frozenset`, :class:`list`, |
| 1163 | :class:`tuple`, and :class:`dict` classes, as well as the :mod:`collections` |
| 1164 | module. |
Georg Brandl | 116aa62 | 2007-08-15 14:28:22 +0000 | [diff] [blame] | 1165 | |
Georg Brandl | 116aa62 | 2007-08-15 14:28:22 +0000 | [diff] [blame] | 1166 | |
| 1167 | .. function:: setattr(object, name, value) |
| 1168 | |
| 1169 | This is the counterpart of :func:`getattr`. The arguments are an object, a |
| 1170 | string and an arbitrary value. The string may name an existing attribute or a |
| 1171 | new attribute. The function assigns the value to the attribute, provided the |
| 1172 | object allows it. For example, ``setattr(x, 'foobar', 123)`` is equivalent to |
| 1173 | ``x.foobar = 123``. |
| 1174 | |
| 1175 | |
Ezio Melotti | e0add76 | 2012-09-14 06:32:35 +0300 | [diff] [blame] | 1176 | .. function:: slice(stop) |
| 1177 | slice(start, stop[, step]) |
Georg Brandl | 116aa62 | 2007-08-15 14:28:22 +0000 | [diff] [blame] | 1178 | |
| 1179 | .. index:: single: Numerical Python |
| 1180 | |
Christian Heimes | d8654cf | 2007-12-02 15:22:16 +0000 | [diff] [blame] | 1181 | Return a :term:`slice` object representing the set of indices specified by |
Georg Brandl | 116aa62 | 2007-08-15 14:28:22 +0000 | [diff] [blame] | 1182 | ``range(start, stop, step)``. The *start* and *step* arguments default to |
| 1183 | ``None``. Slice objects have read-only data attributes :attr:`start`, |
| 1184 | :attr:`stop` and :attr:`step` which merely return the argument values (or their |
| 1185 | default). They have no other explicit functionality; however they are used by |
| 1186 | Numerical Python and other third party extensions. Slice objects are also |
| 1187 | generated when extended indexing syntax is used. For example: |
Raymond Hettinger | cdf8ba3 | 2009-02-19 04:45:07 +0000 | [diff] [blame] | 1188 | ``a[start:stop:step]`` or ``a[start:stop, i]``. See :func:`itertools.islice` |
| 1189 | for an alternate version that returns an iterator. |
Georg Brandl | 116aa62 | 2007-08-15 14:28:22 +0000 | [diff] [blame] | 1190 | |
| 1191 | |
Georg Brandl | 036490d | 2009-05-17 13:00:36 +0000 | [diff] [blame] | 1192 | .. function:: sorted(iterable[, key][, reverse]) |
Georg Brandl | 116aa62 | 2007-08-15 14:28:22 +0000 | [diff] [blame] | 1193 | |
| 1194 | Return a new sorted list from the items in *iterable*. |
| 1195 | |
Raymond Hettinger | 51b9c24 | 2008-02-14 13:52:24 +0000 | [diff] [blame] | 1196 | Has two optional arguments which must be specified as keyword arguments. |
Georg Brandl | 116aa62 | 2007-08-15 14:28:22 +0000 | [diff] [blame] | 1197 | |
Georg Brandl | 116aa62 | 2007-08-15 14:28:22 +0000 | [diff] [blame] | 1198 | *key* specifies a function of one argument that is used to extract a comparison |
Georg Brandl | 1f70cdf | 2010-03-21 09:04:24 +0000 | [diff] [blame] | 1199 | key from each list element: ``key=str.lower``. The default value is ``None`` |
| 1200 | (compare the elements directly). |
Georg Brandl | 116aa62 | 2007-08-15 14:28:22 +0000 | [diff] [blame] | 1201 | |
| 1202 | *reverse* is a boolean value. If set to ``True``, then the list elements are |
| 1203 | sorted as if each comparison were reversed. |
| 1204 | |
Benjamin Peterson | 7ac98ae | 2010-08-17 17:52:02 +0000 | [diff] [blame] | 1205 | Use :func:`functools.cmp_to_key` to convert an old-style *cmp* function to a |
| 1206 | *key* function. |
Georg Brandl | 116aa62 | 2007-08-15 14:28:22 +0000 | [diff] [blame] | 1207 | |
Raymond Hettinger | 46fca07 | 2010-04-02 00:25:45 +0000 | [diff] [blame] | 1208 | For sorting examples and a brief sorting tutorial, see `Sorting HowTo |
| 1209 | <http://wiki.python.org/moin/HowTo/Sorting/>`_\. |
| 1210 | |
Georg Brandl | 116aa62 | 2007-08-15 14:28:22 +0000 | [diff] [blame] | 1211 | .. function:: staticmethod(function) |
| 1212 | |
| 1213 | Return a static method for *function*. |
| 1214 | |
| 1215 | A static method does not receive an implicit first argument. To declare a static |
| 1216 | method, use this idiom:: |
| 1217 | |
| 1218 | class C: |
| 1219 | @staticmethod |
| 1220 | def f(arg1, arg2, ...): ... |
| 1221 | |
Christian Heimes | d8654cf | 2007-12-02 15:22:16 +0000 | [diff] [blame] | 1222 | The ``@staticmethod`` form is a function :term:`decorator` -- see the |
| 1223 | description of function definitions in :ref:`function` for details. |
Georg Brandl | 116aa62 | 2007-08-15 14:28:22 +0000 | [diff] [blame] | 1224 | |
| 1225 | It can be called either on the class (such as ``C.f()``) or on an instance (such |
| 1226 | as ``C().f()``). The instance is ignored except for its class. |
| 1227 | |
Raymond Hettinger | 9028928 | 2011-06-01 16:17:23 -0700 | [diff] [blame] | 1228 | Static methods in Python are similar to those found in Java or C++. Also see |
| 1229 | :func:`classmethod` for a variant that is useful for creating alternate class |
| 1230 | constructors. |
Georg Brandl | 116aa62 | 2007-08-15 14:28:22 +0000 | [diff] [blame] | 1231 | |
| 1232 | For more information on static methods, consult the documentation on the |
| 1233 | standard type hierarchy in :ref:`types`. |
| 1234 | |
Chris Jerdonek | 5fae0e5 | 2012-11-20 17:45:51 -0800 | [diff] [blame] | 1235 | .. index:: |
| 1236 | single: string; str() (built-in function) |
| 1237 | |
Georg Brandl | 116aa62 | 2007-08-15 14:28:22 +0000 | [diff] [blame] | 1238 | |
Nick Coghlan | 83c0ae5 | 2012-08-21 17:42:52 +1000 | [diff] [blame] | 1239 | .. _func-str: |
Chris Jerdonek | 83fe2e1 | 2012-10-07 14:48:36 -0700 | [diff] [blame] | 1240 | .. function:: str(object='') |
Chris Jerdonek | 5fae0e5 | 2012-11-20 17:45:51 -0800 | [diff] [blame] | 1241 | str(object=b'', encoding='utf-8', errors='strict') |
Chris Jerdonek | bb4e941 | 2012-11-28 01:38:40 -0800 | [diff] [blame] | 1242 | :noindex: |
Georg Brandl | 116aa62 | 2007-08-15 14:28:22 +0000 | [diff] [blame] | 1243 | |
Chris Jerdonek | bb4e941 | 2012-11-28 01:38:40 -0800 | [diff] [blame] | 1244 | Return a :class:`str` version of *object*. See :func:`str` for details. |
Georg Brandl | 48310cd | 2009-01-03 21:18:54 +0000 | [diff] [blame] | 1245 | |
Chris Jerdonek | bb4e941 | 2012-11-28 01:38:40 -0800 | [diff] [blame] | 1246 | ``str`` is the built-in string :term:`class`. For general information |
| 1247 | about strings, see :ref:`textseq`. |
Georg Brandl | 116aa62 | 2007-08-15 14:28:22 +0000 | [diff] [blame] | 1248 | |
| 1249 | |
| 1250 | .. function:: sum(iterable[, start]) |
| 1251 | |
| 1252 | Sums *start* and the items of an *iterable* from left to right and returns the |
| 1253 | total. *start* defaults to ``0``. The *iterable*'s items are normally numbers, |
Raymond Hettinger | b373799 | 2010-10-31 21:23:24 +0000 | [diff] [blame] | 1254 | and the start value is not allowed to be a string. |
Georg Brandl | 116aa62 | 2007-08-15 14:28:22 +0000 | [diff] [blame] | 1255 | |
Éric Araujo | 8f9626b | 2010-11-06 06:30:16 +0000 | [diff] [blame] | 1256 | For some use cases, there are good alternatives to :func:`sum`. |
Raymond Hettinger | b373799 | 2010-10-31 21:23:24 +0000 | [diff] [blame] | 1257 | The preferred, fast way to concatenate a sequence of strings is by calling |
| 1258 | ``''.join(sequence)``. To add floating point values with extended precision, |
| 1259 | see :func:`math.fsum`\. To concatenate a series of iterables, consider using |
| 1260 | :func:`itertools.chain`. |
Georg Brandl | 116aa62 | 2007-08-15 14:28:22 +0000 | [diff] [blame] | 1261 | |
Mark Summerfield | 1041f74 | 2008-02-26 13:27:00 +0000 | [diff] [blame] | 1262 | .. function:: super([type[, object-or-type]]) |
Georg Brandl | 116aa62 | 2007-08-15 14:28:22 +0000 | [diff] [blame] | 1263 | |
Raymond Hettinger | 4d9a823 | 2009-02-24 23:30:43 +0000 | [diff] [blame] | 1264 | Return a proxy object that delegates method calls to a parent or sibling |
| 1265 | class of *type*. This is useful for accessing inherited methods that have |
| 1266 | been overridden in a class. The search order is same as that used by |
| 1267 | :func:`getattr` except that the *type* itself is skipped. |
| 1268 | |
Raymond Hettinger | 0a68b01 | 2009-02-25 00:58:47 +0000 | [diff] [blame] | 1269 | The :attr:`__mro__` attribute of the *type* lists the method resolution |
| 1270 | search order used by both :func:`getattr` and :func:`super`. The attribute |
| 1271 | is dynamic and can change whenever the inheritance hierarchy is updated. |
Benjamin Peterson | 3e4f055 | 2008-09-02 00:31:15 +0000 | [diff] [blame] | 1272 | |
Raymond Hettinger | 79d0434 | 2009-02-25 00:32:51 +0000 | [diff] [blame] | 1273 | If the second argument is omitted, the super object returned is unbound. If |
Benjamin Peterson | 9bc9351 | 2008-09-22 22:10:59 +0000 | [diff] [blame] | 1274 | the second argument is an object, ``isinstance(obj, type)`` must be true. If |
Benjamin Peterson | d75fcb4 | 2009-02-19 04:22:03 +0000 | [diff] [blame] | 1275 | the second argument is a type, ``issubclass(type2, type)`` must be true (this |
| 1276 | is useful for classmethods). |
Georg Brandl | 116aa62 | 2007-08-15 14:28:22 +0000 | [diff] [blame] | 1277 | |
Raymond Hettinger | 0a68b01 | 2009-02-25 00:58:47 +0000 | [diff] [blame] | 1278 | There are two typical use cases for *super*. In a class hierarchy with |
| 1279 | single inheritance, *super* can be used to refer to parent classes without |
Benjamin Peterson | 9bc9351 | 2008-09-22 22:10:59 +0000 | [diff] [blame] | 1280 | naming them explicitly, thus making the code more maintainable. This use |
Raymond Hettinger | 0a68b01 | 2009-02-25 00:58:47 +0000 | [diff] [blame] | 1281 | closely parallels the use of *super* in other programming languages. |
Georg Brandl | 48310cd | 2009-01-03 21:18:54 +0000 | [diff] [blame] | 1282 | |
Raymond Hettinger | 4d9a823 | 2009-02-24 23:30:43 +0000 | [diff] [blame] | 1283 | The second use case is to support cooperative multiple inheritance in a |
Georg Brandl | 48310cd | 2009-01-03 21:18:54 +0000 | [diff] [blame] | 1284 | dynamic execution environment. This use case is unique to Python and is |
| 1285 | not found in statically compiled languages or languages that only support |
Raymond Hettinger | d125845 | 2009-02-26 00:27:18 +0000 | [diff] [blame] | 1286 | single inheritance. This makes it possible to implement "diamond diagrams" |
Benjamin Peterson | 9bc9351 | 2008-09-22 22:10:59 +0000 | [diff] [blame] | 1287 | where multiple base classes implement the same method. Good design dictates |
| 1288 | that this method have the same calling signature in every case (because the |
Raymond Hettinger | 4d9a823 | 2009-02-24 23:30:43 +0000 | [diff] [blame] | 1289 | order of calls is determined at runtime, because that order adapts |
| 1290 | to changes in the class hierarchy, and because that order can include |
| 1291 | sibling classes that are unknown prior to runtime). |
Benjamin Peterson | 9bc9351 | 2008-09-22 22:10:59 +0000 | [diff] [blame] | 1292 | |
| 1293 | For both use cases, a typical superclass call looks like this:: |
Georg Brandl | 116aa62 | 2007-08-15 14:28:22 +0000 | [diff] [blame] | 1294 | |
| 1295 | class C(B): |
Mark Summerfield | 1041f74 | 2008-02-26 13:27:00 +0000 | [diff] [blame] | 1296 | def method(self, arg): |
Georg Brandl | 036490d | 2009-05-17 13:00:36 +0000 | [diff] [blame] | 1297 | super().method(arg) # This does the same thing as: |
| 1298 | # super(C, self).method(arg) |
Georg Brandl | 116aa62 | 2007-08-15 14:28:22 +0000 | [diff] [blame] | 1299 | |
| 1300 | Note that :func:`super` is implemented as part of the binding process for |
Mark Summerfield | 1041f74 | 2008-02-26 13:27:00 +0000 | [diff] [blame] | 1301 | explicit dotted attribute lookups such as ``super().__getitem__(name)``. |
Benjamin Peterson | 9bc9351 | 2008-09-22 22:10:59 +0000 | [diff] [blame] | 1302 | It does so by implementing its own :meth:`__getattribute__` method for searching |
Raymond Hettinger | 4d9a823 | 2009-02-24 23:30:43 +0000 | [diff] [blame] | 1303 | classes in a predictable order that supports cooperative multiple inheritance. |
Georg Brandl | 116aa62 | 2007-08-15 14:28:22 +0000 | [diff] [blame] | 1304 | Accordingly, :func:`super` is undefined for implicit lookups using statements or |
Raymond Hettinger | 518d8da | 2008-12-06 11:44:00 +0000 | [diff] [blame] | 1305 | operators such as ``super()[name]``. |
| 1306 | |
Nick Coghlan | 7fc570a | 2012-05-20 02:34:13 +1000 | [diff] [blame] | 1307 | Also note that, aside from the zero argument form, :func:`super` is not |
| 1308 | limited to use inside methods. The two argument form specifies the |
| 1309 | arguments exactly and makes the appropriate references. The zero |
| 1310 | argument form only works inside a class definition, as the compiler fills |
| 1311 | in the necessary details to correctly retrieve the class being defined, |
| 1312 | as well as accessing the current instance for ordinary methods. |
Georg Brandl | 116aa62 | 2007-08-15 14:28:22 +0000 | [diff] [blame] | 1313 | |
Raymond Hettinger | 9028928 | 2011-06-01 16:17:23 -0700 | [diff] [blame] | 1314 | For practical suggestions on how to design cooperative classes using |
| 1315 | :func:`super`, see `guide to using super() |
| 1316 | <http://rhettinger.wordpress.com/2011/05/26/super-considered-super/>`_. |
| 1317 | |
Georg Brandl | 116aa62 | 2007-08-15 14:28:22 +0000 | [diff] [blame] | 1318 | |
Nick Coghlan | 83c0ae5 | 2012-08-21 17:42:52 +1000 | [diff] [blame] | 1319 | .. _func-tuple: |
Georg Brandl | 116aa62 | 2007-08-15 14:28:22 +0000 | [diff] [blame] | 1320 | .. function:: tuple([iterable]) |
Nick Coghlan | 83c0ae5 | 2012-08-21 17:42:52 +1000 | [diff] [blame] | 1321 | :noindex: |
Georg Brandl | 116aa62 | 2007-08-15 14:28:22 +0000 | [diff] [blame] | 1322 | |
Nick Coghlan | 83c0ae5 | 2012-08-21 17:42:52 +1000 | [diff] [blame] | 1323 | Rather than being a function, :class:`tuple` is actually an immutable |
Chris Jerdonek | 006d907 | 2012-10-12 20:28:26 -0700 | [diff] [blame] | 1324 | sequence type, as documented in :ref:`typesseq-tuple` and :ref:`typesseq`. |
Georg Brandl | 116aa62 | 2007-08-15 14:28:22 +0000 | [diff] [blame] | 1325 | |
| 1326 | |
| 1327 | .. function:: type(object) |
Ezio Melotti | 837cd06 | 2012-10-24 23:06:25 +0300 | [diff] [blame] | 1328 | type(name, bases, dict) |
Georg Brandl | 116aa62 | 2007-08-15 14:28:22 +0000 | [diff] [blame] | 1329 | |
| 1330 | .. index:: object: type |
| 1331 | |
Ezio Melotti | 837cd06 | 2012-10-24 23:06:25 +0300 | [diff] [blame] | 1332 | |
| 1333 | With one argument, return the type of an *object*. The return value is a |
| 1334 | type object and generally the same object as returned by ``object.__class__``. |
Georg Brandl | 116aa62 | 2007-08-15 14:28:22 +0000 | [diff] [blame] | 1335 | |
Georg Brandl | 85eb8c1 | 2007-08-31 16:33:38 +0000 | [diff] [blame] | 1336 | The :func:`isinstance` built-in function is recommended for testing the type |
| 1337 | of an object, because it takes subclasses into account. |
| 1338 | |
Georg Brandl | 116aa62 | 2007-08-15 14:28:22 +0000 | [diff] [blame] | 1339 | |
Ezio Melotti | 837cd06 | 2012-10-24 23:06:25 +0300 | [diff] [blame] | 1340 | With three arguments, return a new type object. This is essentially a |
| 1341 | dynamic form of the :keyword:`class` statement. The *name* string is the |
| 1342 | class name and becomes the :attr:`__name__` attribute; the *bases* tuple |
| 1343 | itemizes the base classes and becomes the :attr:`__bases__` attribute; |
| 1344 | and the *dict* dictionary is the namespace containing definitions for class |
| 1345 | body and becomes the :attr:`__dict__` attribute. For example, the |
| 1346 | following two statements create identical :class:`type` objects: |
Georg Brandl | 116aa62 | 2007-08-15 14:28:22 +0000 | [diff] [blame] | 1347 | |
Éric Araujo | 28053fb | 2010-11-22 03:09:19 +0000 | [diff] [blame] | 1348 | >>> class X: |
Georg Brandl | 116aa62 | 2007-08-15 14:28:22 +0000 | [diff] [blame] | 1349 | ... a = 1 |
Georg Brandl | 48310cd | 2009-01-03 21:18:54 +0000 | [diff] [blame] | 1350 | ... |
Georg Brandl | 116aa62 | 2007-08-15 14:28:22 +0000 | [diff] [blame] | 1351 | >>> X = type('X', (object,), dict(a=1)) |
| 1352 | |
Chris Jerdonek | 006d907 | 2012-10-12 20:28:26 -0700 | [diff] [blame] | 1353 | See also :ref:`bltin-type-objects`. |
| 1354 | |
Georg Brandl | 116aa62 | 2007-08-15 14:28:22 +0000 | [diff] [blame] | 1355 | |
| 1356 | .. function:: vars([object]) |
| 1357 | |
Benjamin Peterson | 4ac9ce4 | 2009-10-04 14:49:41 +0000 | [diff] [blame] | 1358 | Without an argument, act like :func:`locals`. |
| 1359 | |
| 1360 | With a module, class or class instance object as argument (or anything else that |
| 1361 | has a :attr:`__dict__` attribute), return that attribute. |
Georg Brandl | 116aa62 | 2007-08-15 14:28:22 +0000 | [diff] [blame] | 1362 | |
Georg Brandl | e720c0a | 2009-04-27 16:20:50 +0000 | [diff] [blame] | 1363 | .. note:: |
Benjamin Peterson | d23f822 | 2009-04-05 19:13:16 +0000 | [diff] [blame] | 1364 | The returned dictionary should not be modified: |
| 1365 | the effects on the corresponding symbol table are undefined. [#]_ |
Georg Brandl | 116aa62 | 2007-08-15 14:28:22 +0000 | [diff] [blame] | 1366 | |
Raymond Hettinger | dd1150e | 2008-03-13 02:39:40 +0000 | [diff] [blame] | 1367 | .. function:: zip(*iterables) |
Georg Brandl | 116aa62 | 2007-08-15 14:28:22 +0000 | [diff] [blame] | 1368 | |
Georg Brandl | 48310cd | 2009-01-03 21:18:54 +0000 | [diff] [blame] | 1369 | Make an iterator that aggregates elements from each of the iterables. |
Raymond Hettinger | dd1150e | 2008-03-13 02:39:40 +0000 | [diff] [blame] | 1370 | |
| 1371 | Returns an iterator of tuples, where the *i*-th tuple contains |
Georg Brandl | 952aea2 | 2007-09-04 17:50:40 +0000 | [diff] [blame] | 1372 | the *i*-th element from each of the argument sequences or iterables. The |
Raymond Hettinger | dd1150e | 2008-03-13 02:39:40 +0000 | [diff] [blame] | 1373 | iterator stops when the shortest input iterable is exhausted. With a single |
Georg Brandl | 48310cd | 2009-01-03 21:18:54 +0000 | [diff] [blame] | 1374 | iterable argument, it returns an iterator of 1-tuples. With no arguments, |
Raymond Hettinger | dd1150e | 2008-03-13 02:39:40 +0000 | [diff] [blame] | 1375 | it returns an empty iterator. Equivalent to:: |
| 1376 | |
Raymond Hettinger | 2f08df3 | 2010-10-10 05:54:39 +0000 | [diff] [blame] | 1377 | def zip(*iterables): |
| 1378 | # zip('ABCD', 'xy') --> Ax By |
| 1379 | sentinel = object() |
Raymond Hettinger | 6f45d18 | 2011-10-30 15:06:14 -0700 | [diff] [blame] | 1380 | iterators = [iter(it) for it in iterables] |
| 1381 | while iterators: |
Raymond Hettinger | 2f08df3 | 2010-10-10 05:54:39 +0000 | [diff] [blame] | 1382 | result = [] |
Raymond Hettinger | 6f45d18 | 2011-10-30 15:06:14 -0700 | [diff] [blame] | 1383 | for it in iterators: |
Raymond Hettinger | 2f08df3 | 2010-10-10 05:54:39 +0000 | [diff] [blame] | 1384 | elem = next(it, sentinel) |
| 1385 | if elem is sentinel: |
| 1386 | return |
| 1387 | result.append(elem) |
| 1388 | yield tuple(result) |
Georg Brandl | 116aa62 | 2007-08-15 14:28:22 +0000 | [diff] [blame] | 1389 | |
Christian Heimes | 1af737c | 2008-01-23 08:24:23 +0000 | [diff] [blame] | 1390 | The left-to-right evaluation order of the iterables is guaranteed. This |
| 1391 | makes possible an idiom for clustering a data series into n-length groups |
| 1392 | using ``zip(*[iter(s)]*n)``. |
| 1393 | |
Raymond Hettinger | dd1150e | 2008-03-13 02:39:40 +0000 | [diff] [blame] | 1394 | :func:`zip` should only be used with unequal length inputs when you don't |
| 1395 | care about trailing, unmatched values from the longer iterables. If those |
| 1396 | values are important, use :func:`itertools.zip_longest` instead. |
Georg Brandl | 116aa62 | 2007-08-15 14:28:22 +0000 | [diff] [blame] | 1397 | |
Benjamin Peterson | f10a79a | 2008-10-11 00:49:57 +0000 | [diff] [blame] | 1398 | :func:`zip` in conjunction with the ``*`` operator can be used to unzip a |
| 1399 | list:: |
| 1400 | |
| 1401 | >>> x = [1, 2, 3] |
| 1402 | >>> y = [4, 5, 6] |
| 1403 | >>> zipped = zip(x, y) |
Georg Brandl | 17fe364 | 2008-12-06 14:28:56 +0000 | [diff] [blame] | 1404 | >>> list(zipped) |
Benjamin Peterson | f10a79a | 2008-10-11 00:49:57 +0000 | [diff] [blame] | 1405 | [(1, 4), (2, 5), (3, 6)] |
Georg Brandl | 17fe364 | 2008-12-06 14:28:56 +0000 | [diff] [blame] | 1406 | >>> x2, y2 = zip(*zip(x, y)) |
Benjamin Peterson | fa0d703 | 2009-06-01 22:42:33 +0000 | [diff] [blame] | 1407 | >>> x == list(x2) and y == list(y2) |
Benjamin Peterson | f10a79a | 2008-10-11 00:49:57 +0000 | [diff] [blame] | 1408 | True |
| 1409 | |
Georg Brandl | 2ee470f | 2008-07-16 12:55:28 +0000 | [diff] [blame] | 1410 | |
Brett Cannon | cb4996a | 2012-08-06 16:34:44 -0400 | [diff] [blame] | 1411 | .. function:: __import__(name, globals=None, locals=None, fromlist=(), level=0) |
Georg Brandl | 4836781 | 2008-12-05 15:55:41 +0000 | [diff] [blame] | 1412 | |
| 1413 | .. index:: |
| 1414 | statement: import |
| 1415 | module: imp |
| 1416 | |
| 1417 | .. note:: |
| 1418 | |
| 1419 | This is an advanced function that is not needed in everyday Python |
Éric Araujo | e801aa2 | 2011-07-29 17:50:58 +0200 | [diff] [blame] | 1420 | programming, unlike :func:`importlib.import_module`. |
Georg Brandl | 4836781 | 2008-12-05 15:55:41 +0000 | [diff] [blame] | 1421 | |
Benjamin Peterson | 6ebe78f | 2008-12-21 00:06:59 +0000 | [diff] [blame] | 1422 | This function is invoked by the :keyword:`import` statement. It can be |
| 1423 | replaced (by importing the :mod:`builtins` module and assigning to |
| 1424 | ``builtins.__import__``) in order to change semantics of the |
| 1425 | :keyword:`import` statement, but nowadays it is usually simpler to use import |
Brett Cannon | 2a082ad | 2012-04-14 21:58:33 -0400 | [diff] [blame] | 1426 | hooks (see :pep:`302`) to attain the same goals. Direct use of |
| 1427 | :func:`__import__` is entirely discouraged in favor of |
| 1428 | :func:`importlib.import_module`. |
Georg Brandl | 4836781 | 2008-12-05 15:55:41 +0000 | [diff] [blame] | 1429 | |
Benjamin Peterson | 6ebe78f | 2008-12-21 00:06:59 +0000 | [diff] [blame] | 1430 | The function imports the module *name*, potentially using the given *globals* |
| 1431 | and *locals* to determine how to interpret the name in a package context. |
| 1432 | The *fromlist* gives the names of objects or submodules that should be |
| 1433 | imported from the module given by *name*. The standard implementation does |
| 1434 | not use its *locals* argument at all, and uses its *globals* only to |
| 1435 | determine the package context of the :keyword:`import` statement. |
| 1436 | |
Brett Cannon | 2b9fd47 | 2009-03-15 02:18:41 +0000 | [diff] [blame] | 1437 | *level* specifies whether to use absolute or relative imports. ``0`` (the |
| 1438 | default) means only perform absolute imports. Positive values for |
Benjamin Peterson | 6ebe78f | 2008-12-21 00:06:59 +0000 | [diff] [blame] | 1439 | *level* indicate the number of parent directories to search relative to the |
Brett Cannon | 2a082ad | 2012-04-14 21:58:33 -0400 | [diff] [blame] | 1440 | directory of the module calling :func:`__import__` (see :pep:`328` for the |
| 1441 | details). |
Georg Brandl | 4836781 | 2008-12-05 15:55:41 +0000 | [diff] [blame] | 1442 | |
| 1443 | When the *name* variable is of the form ``package.module``, normally, the |
| 1444 | top-level package (the name up till the first dot) is returned, *not* the |
| 1445 | module named by *name*. However, when a non-empty *fromlist* argument is |
Benjamin Peterson | 6ebe78f | 2008-12-21 00:06:59 +0000 | [diff] [blame] | 1446 | given, the module named by *name* is returned. |
Georg Brandl | 4836781 | 2008-12-05 15:55:41 +0000 | [diff] [blame] | 1447 | |
Benjamin Peterson | 6ebe78f | 2008-12-21 00:06:59 +0000 | [diff] [blame] | 1448 | For example, the statement ``import spam`` results in bytecode resembling the |
| 1449 | following code:: |
Georg Brandl | 48310cd | 2009-01-03 21:18:54 +0000 | [diff] [blame] | 1450 | |
Brett Cannon | 2b9fd47 | 2009-03-15 02:18:41 +0000 | [diff] [blame] | 1451 | spam = __import__('spam', globals(), locals(), [], 0) |
Georg Brandl | 4836781 | 2008-12-05 15:55:41 +0000 | [diff] [blame] | 1452 | |
Benjamin Peterson | 6ebe78f | 2008-12-21 00:06:59 +0000 | [diff] [blame] | 1453 | The statement ``import spam.ham`` results in this call:: |
Georg Brandl | 4836781 | 2008-12-05 15:55:41 +0000 | [diff] [blame] | 1454 | |
Brett Cannon | 2b9fd47 | 2009-03-15 02:18:41 +0000 | [diff] [blame] | 1455 | spam = __import__('spam.ham', globals(), locals(), [], 0) |
Benjamin Peterson | 6ebe78f | 2008-12-21 00:06:59 +0000 | [diff] [blame] | 1456 | |
| 1457 | Note how :func:`__import__` returns the toplevel module here because this is |
| 1458 | the object that is bound to a name by the :keyword:`import` statement. |
| 1459 | |
| 1460 | On the other hand, the statement ``from spam.ham import eggs, sausage as |
| 1461 | saus`` results in :: |
| 1462 | |
Brett Cannon | 2b9fd47 | 2009-03-15 02:18:41 +0000 | [diff] [blame] | 1463 | _temp = __import__('spam.ham', globals(), locals(), ['eggs', 'sausage'], 0) |
Benjamin Peterson | 6ebe78f | 2008-12-21 00:06:59 +0000 | [diff] [blame] | 1464 | eggs = _temp.eggs |
| 1465 | saus = _temp.sausage |
| 1466 | |
| 1467 | Here, the ``spam.ham`` module is returned from :func:`__import__`. From this |
| 1468 | object, the names to import are retrieved and assigned to their respective |
| 1469 | names. |
| 1470 | |
| 1471 | If you simply want to import a module (potentially within a package) by name, |
Éric Araujo | e801aa2 | 2011-07-29 17:50:58 +0200 | [diff] [blame] | 1472 | use :func:`importlib.import_module`. |
Benjamin Peterson | 6ebe78f | 2008-12-21 00:06:59 +0000 | [diff] [blame] | 1473 | |
Brett Cannon | 73df364 | 2012-07-30 18:35:17 -0400 | [diff] [blame] | 1474 | .. versionchanged:: 3.3 |
Brett Cannon | 222d473 | 2012-08-05 20:49:53 -0400 | [diff] [blame] | 1475 | Negative values for *level* are no longer supported (which also changes |
| 1476 | the default value to 0). |
Brett Cannon | 73df364 | 2012-07-30 18:35:17 -0400 | [diff] [blame] | 1477 | |
Georg Brandl | 4836781 | 2008-12-05 15:55:41 +0000 | [diff] [blame] | 1478 | |
Georg Brandl | 116aa62 | 2007-08-15 14:28:22 +0000 | [diff] [blame] | 1479 | .. rubric:: Footnotes |
| 1480 | |
Georg Brandl | 47f27a3 | 2009-03-31 16:57:13 +0000 | [diff] [blame] | 1481 | .. [#] Note that the parser only accepts the Unix-style end of line convention. |
| 1482 | If you are reading the code from a file, make sure to use newline conversion |
| 1483 | mode to convert Windows or Mac-style newlines. |
Georg Brandl | 116aa62 | 2007-08-15 14:28:22 +0000 | [diff] [blame] | 1484 | |
| 1485 | .. [#] In the current implementation, local variable bindings cannot normally be |
| 1486 | affected this way, but variables retrieved from other scopes (such as modules) |
| 1487 | can be. This may change. |