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 | |
| 10 | |
Georg Brandl | 116aa62 | 2007-08-15 14:28:22 +0000 | [diff] [blame] | 11 | .. function:: abs(x) |
| 12 | |
Georg Brandl | ba956ae | 2007-11-29 17:24:34 +0000 | [diff] [blame] | 13 | Return the absolute value of a number. The argument may be an |
Georg Brandl | 116aa62 | 2007-08-15 14:28:22 +0000 | [diff] [blame] | 14 | integer or a floating point number. If the argument is a complex number, its |
| 15 | magnitude is returned. |
| 16 | |
| 17 | |
| 18 | .. function:: all(iterable) |
| 19 | |
Georg Brandl | 0192bff | 2009-04-27 16:49:41 +0000 | [diff] [blame] | 20 | Return True if all elements of the *iterable* are true (or if the iterable |
| 21 | is empty). Equivalent to:: |
Georg Brandl | 116aa62 | 2007-08-15 14:28:22 +0000 | [diff] [blame] | 22 | |
| 23 | def all(iterable): |
| 24 | for element in iterable: |
| 25 | if not element: |
| 26 | return False |
| 27 | return True |
| 28 | |
Georg Brandl | 116aa62 | 2007-08-15 14:28:22 +0000 | [diff] [blame] | 29 | |
| 30 | .. function:: any(iterable) |
| 31 | |
Georg Brandl | 0192bff | 2009-04-27 16:49:41 +0000 | [diff] [blame] | 32 | Return True if any element of the *iterable* is true. If the iterable |
| 33 | is empty, return False. Equivalent to:: |
Georg Brandl | 116aa62 | 2007-08-15 14:28:22 +0000 | [diff] [blame] | 34 | |
| 35 | def any(iterable): |
| 36 | for element in iterable: |
| 37 | if element: |
| 38 | return True |
| 39 | return False |
| 40 | |
Georg Brandl | 116aa62 | 2007-08-15 14:28:22 +0000 | [diff] [blame] | 41 | |
Georg Brandl | 559e5d7 | 2008-06-11 18:37:52 +0000 | [diff] [blame] | 42 | .. function:: ascii(object) |
| 43 | |
| 44 | As :func:`repr`, return a string containing a printable representation of an |
| 45 | object, but escape the non-ASCII characters in the string returned by |
| 46 | :func:`repr` using ``\x``, ``\u`` or ``\U`` escapes. This generates a string |
| 47 | similar to that returned by :func:`repr` in Python 2. |
| 48 | |
| 49 | |
Georg Brandl | 116aa62 | 2007-08-15 14:28:22 +0000 | [diff] [blame] | 50 | .. function:: bin(x) |
| 51 | |
| 52 | Convert an integer number to a binary string. The result is a valid Python |
| 53 | expression. If *x* is not a Python :class:`int` object, it has to define an |
| 54 | :meth:`__index__` method that returns an integer. |
| 55 | |
Georg Brandl | 116aa62 | 2007-08-15 14:28:22 +0000 | [diff] [blame] | 56 | |
| 57 | .. function:: bool([x]) |
| 58 | |
| 59 | Convert a value to a Boolean, using the standard truth testing procedure. If |
| 60 | *x* is false or omitted, this returns :const:`False`; otherwise it returns |
| 61 | :const:`True`. :class:`bool` is also a class, which is a subclass of |
| 62 | :class:`int`. Class :class:`bool` cannot be subclassed further. Its only |
| 63 | instances are :const:`False` and :const:`True`. |
| 64 | |
| 65 | .. index:: pair: Boolean; type |
| 66 | |
Georg Brandl | 116aa62 | 2007-08-15 14:28:22 +0000 | [diff] [blame] | 67 | |
Georg Brandl | 036490d | 2009-05-17 13:00:36 +0000 | [diff] [blame] | 68 | .. function:: bytearray([source[, encoding[, errors]]]) |
Georg Brandl | 85eb8c1 | 2007-08-31 16:33:38 +0000 | [diff] [blame] | 69 | |
Georg Brandl | 24eac03 | 2007-11-22 14:16:00 +0000 | [diff] [blame] | 70 | 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] | 71 | sequence of integers in the range 0 <= x < 256. It has most of the usual |
| 72 | methods of mutable sequences, described in :ref:`typesseq-mutable`, as well |
| 73 | as most methods that the :class:`str` type has, see :ref:`bytes-methods`. |
Georg Brandl | 85eb8c1 | 2007-08-31 16:33:38 +0000 | [diff] [blame] | 74 | |
Georg Brandl | 036490d | 2009-05-17 13:00:36 +0000 | [diff] [blame] | 75 | 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] | 76 | different ways: |
| 77 | |
| 78 | * 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] | 79 | *errors*) parameters; :func:`bytearray` then converts the string to |
Guido van Rossum | 98297ee | 2007-11-06 21:34:58 +0000 | [diff] [blame] | 80 | bytes using :meth:`str.encode`. |
Georg Brandl | 85eb8c1 | 2007-08-31 16:33:38 +0000 | [diff] [blame] | 81 | |
| 82 | * If it is an *integer*, the array will have that size and will be |
| 83 | initialized with null bytes. |
| 84 | |
| 85 | * If it is an object conforming to the *buffer* interface, a read-only buffer |
| 86 | of the object will be used to initialize the bytes array. |
| 87 | |
Guido van Rossum | 98297ee | 2007-11-06 21:34:58 +0000 | [diff] [blame] | 88 | * If it is an *iterable*, it must be an iterable of integers in the range |
| 89 | ``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] | 90 | |
| 91 | Without an argument, an array of size 0 is created. |
| 92 | |
| 93 | |
Georg Brandl | 036490d | 2009-05-17 13:00:36 +0000 | [diff] [blame] | 94 | .. function:: bytes([source[, encoding[, errors]]]) |
Guido van Rossum | 98297ee | 2007-11-06 21:34:58 +0000 | [diff] [blame] | 95 | |
| 96 | Return a new "bytes" object, which is an immutable sequence of integers in |
| 97 | the range ``0 <= x < 256``. :class:`bytes` is an immutable version of |
Georg Brandl | 9541463 | 2007-11-22 11:00:28 +0000 | [diff] [blame] | 98 | :class:`bytearray` -- it has the same non-mutating methods and the same |
| 99 | indexing and slicing behavior. |
Georg Brandl | 48310cd | 2009-01-03 21:18:54 +0000 | [diff] [blame] | 100 | |
Georg Brandl | 476b355 | 2009-04-29 06:37:12 +0000 | [diff] [blame] | 101 | Accordingly, constructor arguments are interpreted as for :func:`bytearray`. |
Guido van Rossum | 98297ee | 2007-11-06 21:34:58 +0000 | [diff] [blame] | 102 | |
| 103 | Bytes objects can also be created with literals, see :ref:`strings`. |
| 104 | |
| 105 | |
Georg Brandl | 116aa62 | 2007-08-15 14:28:22 +0000 | [diff] [blame] | 106 | .. function:: chr(i) |
| 107 | |
Georg Brandl | 85eb8c1 | 2007-08-31 16:33:38 +0000 | [diff] [blame] | 108 | Return the string of one character whose Unicode codepoint is the integer |
| 109 | *i*. For example, ``chr(97)`` returns the string ``'a'``. This is the |
| 110 | inverse of :func:`ord`. The valid range for the argument depends how Python |
| 111 | was configured -- it may be either UCS2 [0..0xFFFF] or UCS4 [0..0x10FFFF]. |
Georg Brandl | 116aa62 | 2007-08-15 14:28:22 +0000 | [diff] [blame] | 112 | :exc:`ValueError` will be raised if *i* is outside that range. |
| 113 | |
| 114 | |
| 115 | .. function:: classmethod(function) |
| 116 | |
| 117 | Return a class method for *function*. |
| 118 | |
| 119 | A class method receives the class as implicit first argument, just like an |
| 120 | instance method receives the instance. To declare a class method, use this |
| 121 | idiom:: |
| 122 | |
| 123 | class C: |
| 124 | @classmethod |
| 125 | def f(cls, arg1, arg2, ...): ... |
| 126 | |
Christian Heimes | d8654cf | 2007-12-02 15:22:16 +0000 | [diff] [blame] | 127 | The ``@classmethod`` form is a function :term:`decorator` -- see the description |
| 128 | of function definitions in :ref:`function` for details. |
Georg Brandl | 116aa62 | 2007-08-15 14:28:22 +0000 | [diff] [blame] | 129 | |
| 130 | It can be called either on the class (such as ``C.f()``) or on an instance (such |
| 131 | as ``C().f()``). The instance is ignored except for its class. If a class |
| 132 | method is called for a derived class, the derived class object is passed as the |
| 133 | implied first argument. |
| 134 | |
| 135 | Class methods are different than C++ or Java static methods. If you want those, |
| 136 | see :func:`staticmethod` in this section. |
| 137 | |
| 138 | For more information on class methods, consult the documentation on the standard |
| 139 | type hierarchy in :ref:`types`. |
| 140 | |
Georg Brandl | 116aa62 | 2007-08-15 14:28:22 +0000 | [diff] [blame] | 141 | |
Georg Brandl | 036490d | 2009-05-17 13:00:36 +0000 | [diff] [blame] | 142 | .. function:: compile(source, filename, mode, flags=0, dont_inherit=False) |
Georg Brandl | 116aa62 | 2007-08-15 14:28:22 +0000 | [diff] [blame] | 143 | |
Benjamin Peterson | ec9199b | 2008-11-08 17:05:00 +0000 | [diff] [blame] | 144 | Compile the *source* into a code or AST object. Code objects can be executed |
| 145 | by an :keyword:`exec` statement or evaluated by a call to :func:`eval`. |
| 146 | *source* can either be a string or an AST object. Refer to the :mod:`ast` |
| 147 | module documentation for information on how to work with AST objects. |
Georg Brandl | 116aa62 | 2007-08-15 14:28:22 +0000 | [diff] [blame] | 148 | |
Benjamin Peterson | ec9199b | 2008-11-08 17:05:00 +0000 | [diff] [blame] | 149 | The *filename* argument should give the file from which the code was read; |
| 150 | pass some recognizable value if it wasn't read from a file (``'<string>'`` is |
| 151 | commonly used). |
| 152 | |
| 153 | The *mode* argument specifies what kind of code must be compiled; it can be |
| 154 | ``'exec'`` if *source* consists of a sequence of statements, ``'eval'`` if it |
| 155 | consists of a single expression, or ``'single'`` if it consists of a single |
| 156 | interactive statement (in the latter case, expression statements that |
| 157 | evaluate to something else than ``None`` will be printed). |
Georg Brandl | 116aa62 | 2007-08-15 14:28:22 +0000 | [diff] [blame] | 158 | |
Georg Brandl | e06de8b | 2008-05-05 21:42:51 +0000 | [diff] [blame] | 159 | The optional arguments *flags* and *dont_inherit* control which future |
| 160 | statements (see :pep:`236`) affect the compilation of *source*. If neither |
| 161 | is present (or both are zero) the code is compiled with those future |
| 162 | statements that are in effect in the code that is calling compile. If the |
| 163 | *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] | 164 | future statements specified by the *flags* argument are used in addition to |
| 165 | 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] | 166 | the *flags* argument is it -- the future statements in effect around the call |
| 167 | to compile are ignored. |
Georg Brandl | 116aa62 | 2007-08-15 14:28:22 +0000 | [diff] [blame] | 168 | |
Christian Heimes | faf2f63 | 2008-01-06 16:59:19 +0000 | [diff] [blame] | 169 | 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] | 170 | specify multiple statements. The bitfield required to specify a given feature |
| 171 | can be found as the :attr:`compiler_flag` attribute on the :class:`_Feature` |
| 172 | instance in the :mod:`__future__` module. |
| 173 | |
Christian Heimes | 7f04431 | 2008-01-06 17:05:40 +0000 | [diff] [blame] | 174 | This function raises :exc:`SyntaxError` if the compiled source is invalid, |
| 175 | and :exc:`TypeError` if the source contains null bytes. |
| 176 | |
Benjamin Peterson | ec9199b | 2008-11-08 17:05:00 +0000 | [diff] [blame] | 177 | .. note:: |
| 178 | |
| 179 | When compiling a string with multi-line statements, line endings must be |
| 180 | represented by a single newline character (``'\n'``), and the input must |
| 181 | be terminated by at least one newline character. If line endings are |
| 182 | represented by ``'\r\n'``, use :meth:`str.replace` to change them into |
| 183 | ``'\n'``. |
| 184 | |
Georg Brandl | 116aa62 | 2007-08-15 14:28:22 +0000 | [diff] [blame] | 185 | |
| 186 | .. function:: complex([real[, imag]]) |
| 187 | |
| 188 | Create a complex number with the value *real* + *imag*\*j or convert a string or |
| 189 | number to a complex number. If the first parameter is a string, it will be |
| 190 | interpreted as a complex number and the function must be called without a second |
| 191 | parameter. The second parameter can never be a string. Each argument may be any |
| 192 | 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] | 193 | the function serves as a numeric conversion function like :func:`int` |
| 194 | and :func:`float`. If both arguments are omitted, returns ``0j``. |
Georg Brandl | 116aa62 | 2007-08-15 14:28:22 +0000 | [diff] [blame] | 195 | |
| 196 | The complex type is described in :ref:`typesnumeric`. |
| 197 | |
| 198 | |
| 199 | .. function:: delattr(object, name) |
| 200 | |
| 201 | This is a relative of :func:`setattr`. The arguments are an object and a |
| 202 | string. The string must be the name of one of the object's attributes. The |
| 203 | function deletes the named attribute, provided the object allows it. For |
| 204 | example, ``delattr(x, 'foobar')`` is equivalent to ``del x.foobar``. |
| 205 | |
| 206 | |
| 207 | .. function:: dict([arg]) |
| 208 | :noindex: |
| 209 | |
| 210 | Create a new data dictionary, optionally with items taken from *arg*. |
| 211 | The dictionary type is described in :ref:`typesmapping`. |
| 212 | |
| 213 | For other containers see the built in :class:`list`, :class:`set`, and |
| 214 | :class:`tuple` classes, and the :mod:`collections` module. |
| 215 | |
| 216 | |
| 217 | .. function:: dir([object]) |
| 218 | |
| 219 | Without arguments, return the list of names in the current local scope. With an |
| 220 | argument, attempt to return a list of valid attributes for that object. |
| 221 | |
| 222 | If the object has a method named :meth:`__dir__`, this method will be called and |
| 223 | must return the list of attributes. This allows objects that implement a custom |
| 224 | :func:`__getattr__` or :func:`__getattribute__` function to customize the way |
| 225 | :func:`dir` reports their attributes. |
| 226 | |
| 227 | If the object does not provide :meth:`__dir__`, the function tries its best to |
| 228 | gather information from the object's :attr:`__dict__` attribute, if defined, and |
| 229 | from its type object. The resulting list is not necessarily complete, and may |
| 230 | be inaccurate when the object has a custom :func:`__getattr__`. |
| 231 | |
| 232 | The default :func:`dir` mechanism behaves differently with different types of |
| 233 | objects, as it attempts to produce the most relevant, rather than complete, |
| 234 | information: |
| 235 | |
| 236 | * If the object is a module object, the list contains the names of the module's |
| 237 | attributes. |
| 238 | |
| 239 | * If the object is a type or class object, the list contains the names of its |
| 240 | attributes, and recursively of the attributes of its bases. |
| 241 | |
| 242 | * Otherwise, the list contains the object's attributes' names, the names of its |
| 243 | class's attributes, and recursively of the attributes of its class's base |
| 244 | classes. |
| 245 | |
Christian Heimes | fe337bf | 2008-03-23 21:54:12 +0000 | [diff] [blame] | 246 | The resulting list is sorted alphabetically. For example: |
| 247 | |
| 248 | >>> import struct |
| 249 | >>> dir() # doctest: +SKIP |
| 250 | ['__builtins__', '__doc__', '__name__', 'struct'] |
| 251 | >>> dir(struct) # doctest: +NORMALIZE_WHITESPACE |
| 252 | ['Struct', '__builtins__', '__doc__', '__file__', '__name__', |
| 253 | '__package__', '_clearcache', 'calcsize', 'error', 'pack', 'pack_into', |
| 254 | 'unpack', 'unpack_from'] |
| 255 | >>> class Foo(object): |
| 256 | ... def __dir__(self): |
| 257 | ... return ["kan", "ga", "roo"] |
| 258 | ... |
| 259 | >>> f = Foo() |
| 260 | >>> dir(f) |
| 261 | ['ga', 'kan', 'roo'] |
Georg Brandl | 116aa62 | 2007-08-15 14:28:22 +0000 | [diff] [blame] | 262 | |
| 263 | .. note:: |
| 264 | |
| 265 | 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] | 266 | interactive prompt, it tries to supply an interesting set of names more |
| 267 | than it tries to supply a rigorously or consistently defined set of names, |
| 268 | and its detailed behavior may change across releases. For example, |
| 269 | metaclass attributes are not in the result list when the argument is a |
| 270 | class. |
Georg Brandl | 116aa62 | 2007-08-15 14:28:22 +0000 | [diff] [blame] | 271 | |
| 272 | |
| 273 | .. function:: divmod(a, b) |
| 274 | |
| 275 | 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] | 276 | consisting of their quotient and remainder when using integer division. With |
| 277 | mixed operand types, the rules for binary arithmetic operators apply. For |
| 278 | integers, the result is the same as ``(a // b, a % b)``. For floating point |
| 279 | numbers the result is ``(q, a % b)``, where *q* is usually ``math.floor(a / |
| 280 | b)`` but may be 1 less than that. In any case ``q * b + a % b`` is very |
| 281 | close to *a*, if ``a % b`` is non-zero it has the same sign as *b*, and ``0 |
| 282 | <= abs(a % b) < abs(b)``. |
Georg Brandl | 116aa62 | 2007-08-15 14:28:22 +0000 | [diff] [blame] | 283 | |
Georg Brandl | 116aa62 | 2007-08-15 14:28:22 +0000 | [diff] [blame] | 284 | |
Georg Brandl | 036490d | 2009-05-17 13:00:36 +0000 | [diff] [blame] | 285 | .. function:: enumerate(iterable, start=0) |
Georg Brandl | 116aa62 | 2007-08-15 14:28:22 +0000 | [diff] [blame] | 286 | |
Georg Brandl | d11ae5d | 2008-05-16 13:27:32 +0000 | [diff] [blame] | 287 | Return an enumerate object. *iterable* must be a sequence, an |
Alexandre Vassalotti | eca20b6 | 2008-05-16 02:54:33 +0000 | [diff] [blame] | 288 | :term:`iterator`, or some other object which supports iteration. The |
| 289 | :meth:`__next__` method of the iterator returned by :func:`enumerate` returns a |
Alexandre Vassalotti | e9f305f | 2008-05-16 04:39:54 +0000 | [diff] [blame] | 290 | tuple containing a count (from *start* which defaults to 0) and the |
| 291 | corresponding value obtained from iterating over *iterable*. |
| 292 | :func:`enumerate` is useful for obtaining an indexed series: ``(0, seq[0])``, |
| 293 | ``(1, seq[1])``, ``(2, seq[2])``, .... For example: |
Georg Brandl | 116aa62 | 2007-08-15 14:28:22 +0000 | [diff] [blame] | 294 | |
Benjamin Peterson | c9928cc | 2008-12-20 03:20:23 +0000 | [diff] [blame] | 295 | >>> for i, season in enumerate(['Spring', 'Summer', 'Fall', 'Winter']): |
Christian Heimes | fe337bf | 2008-03-23 21:54:12 +0000 | [diff] [blame] | 296 | ... print(i, season) |
Georg Brandl | 116aa62 | 2007-08-15 14:28:22 +0000 | [diff] [blame] | 297 | 0 Spring |
| 298 | 1 Summer |
| 299 | 2 Fall |
| 300 | 3 Winter |
| 301 | |
Georg Brandl | 116aa62 | 2007-08-15 14:28:22 +0000 | [diff] [blame] | 302 | |
Georg Brandl | 036490d | 2009-05-17 13:00:36 +0000 | [diff] [blame] | 303 | .. function:: eval(expression, globals=None, locals=None) |
Georg Brandl | 116aa62 | 2007-08-15 14:28:22 +0000 | [diff] [blame] | 304 | |
| 305 | The arguments are a string and optional globals and locals. If provided, |
| 306 | *globals* must be a dictionary. If provided, *locals* can be any mapping |
| 307 | object. |
| 308 | |
Georg Brandl | 116aa62 | 2007-08-15 14:28:22 +0000 | [diff] [blame] | 309 | The *expression* argument is parsed and evaluated as a Python expression |
| 310 | (technically speaking, a condition list) using the *globals* and *locals* |
Georg Brandl | 9afde1c | 2007-11-01 20:32:30 +0000 | [diff] [blame] | 311 | dictionaries as global and local namespace. If the *globals* dictionary is |
Georg Brandl | 116aa62 | 2007-08-15 14:28:22 +0000 | [diff] [blame] | 312 | present and lacks '__builtins__', the current globals are copied into *globals* |
| 313 | before *expression* is parsed. This means that *expression* normally has full |
Georg Brandl | 1a3284e | 2007-12-02 09:40:06 +0000 | [diff] [blame] | 314 | access to the standard :mod:`builtins` module and restricted environments are |
Georg Brandl | 116aa62 | 2007-08-15 14:28:22 +0000 | [diff] [blame] | 315 | propagated. If the *locals* dictionary is omitted it defaults to the *globals* |
| 316 | dictionary. If both dictionaries are omitted, the expression is executed in the |
Christian Heimes | 5b5e81c | 2007-12-31 16:14:33 +0000 | [diff] [blame] | 317 | 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] | 318 | the evaluated expression. Syntax errors are reported as exceptions. Example: |
Georg Brandl | 116aa62 | 2007-08-15 14:28:22 +0000 | [diff] [blame] | 319 | |
| 320 | >>> x = 1 |
Georg Brandl | 6911e3c | 2007-09-04 07:15:32 +0000 | [diff] [blame] | 321 | >>> eval('x+1') |
Georg Brandl | 116aa62 | 2007-08-15 14:28:22 +0000 | [diff] [blame] | 322 | 2 |
| 323 | |
Benjamin Peterson | 3e4f055 | 2008-09-02 00:31:15 +0000 | [diff] [blame] | 324 | This function can also be used to execute arbitrary code objects (such as |
| 325 | those created by :func:`compile`). In this case pass a code object instead |
| 326 | of a string. If the code object has been compiled with ``'exec'`` as the |
| 327 | *kind* argument, :func:`eval`\'s return value will be ``None``. |
Georg Brandl | 116aa62 | 2007-08-15 14:28:22 +0000 | [diff] [blame] | 328 | |
| 329 | Hints: dynamic execution of statements is supported by the :func:`exec` |
| 330 | function. The :func:`globals` and :func:`locals` functions |
| 331 | returns the current global and local dictionary, respectively, which may be |
| 332 | useful to pass around for use by :func:`eval` or :func:`exec`. |
| 333 | |
| 334 | |
| 335 | .. function:: exec(object[, globals[, locals]]) |
| 336 | |
Benjamin Peterson | d3013ff | 2008-11-11 21:43:42 +0000 | [diff] [blame] | 337 | This function supports dynamic execution of Python code. *object* must be |
| 338 | either a string or a code object. If it is a string, the string is parsed as |
| 339 | 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] | 340 | occurs). [#]_ If it is a code object, it is simply executed. In all cases, |
| 341 | the code that's executed is expected to be valid as file input (see the |
| 342 | section "File input" in the Reference Manual). Be aware that the |
| 343 | :keyword:`return` and :keyword:`yield` statements may not be used outside of |
| 344 | function definitions even within the context of code passed to the |
| 345 | :func:`exec` function. The return value is ``None``. |
Georg Brandl | 116aa62 | 2007-08-15 14:28:22 +0000 | [diff] [blame] | 346 | |
| 347 | In all cases, if the optional parts are omitted, the code is executed in the |
| 348 | current scope. If only *globals* is provided, it must be a dictionary, which |
| 349 | will be used for both the global and the local variables. If *globals* and |
| 350 | *locals* are given, they are used for the global and local variables, |
| 351 | respectively. If provided, *locals* can be any mapping object. |
| 352 | |
| 353 | If the *globals* dictionary does not contain a value for the key |
| 354 | ``__builtins__``, a reference to the dictionary of the built-in module |
Georg Brandl | 1a3284e | 2007-12-02 09:40:06 +0000 | [diff] [blame] | 355 | :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] | 356 | builtins are available to the executed code by inserting your own |
| 357 | ``__builtins__`` dictionary into *globals* before passing it to :func:`exec`. |
| 358 | |
| 359 | .. note:: |
| 360 | |
| 361 | The built-in functions :func:`globals` and :func:`locals` return the current |
| 362 | global and local dictionary, respectively, which may be useful to pass around |
| 363 | for use as the second and third argument to :func:`exec`. |
| 364 | |
Georg Brandl | e720c0a | 2009-04-27 16:20:50 +0000 | [diff] [blame] | 365 | .. note:: |
Georg Brandl | 116aa62 | 2007-08-15 14:28:22 +0000 | [diff] [blame] | 366 | |
| 367 | The default *locals* act as described for function :func:`locals` below: |
Georg Brandl | f694518 | 2008-02-01 11:56:49 +0000 | [diff] [blame] | 368 | modifications to the default *locals* dictionary should not be attempted. |
| 369 | Pass an explicit *locals* dictionary if you need to see effects of the |
| 370 | code on *locals* after function :func:`exec` returns. |
Georg Brandl | 116aa62 | 2007-08-15 14:28:22 +0000 | [diff] [blame] | 371 | |
| 372 | |
| 373 | .. function:: filter(function, iterable) |
| 374 | |
Georg Brandl | 952aea2 | 2007-09-04 17:50:40 +0000 | [diff] [blame] | 375 | Construct an iterator from those elements of *iterable* for which *function* |
| 376 | returns true. *iterable* may be either a sequence, a container which |
Georg Brandl | 9afde1c | 2007-11-01 20:32:30 +0000 | [diff] [blame] | 377 | supports iteration, or an iterator. If *function* is ``None``, the identity |
| 378 | function is assumed, that is, all elements of *iterable* that are false are |
| 379 | removed. |
Georg Brandl | 116aa62 | 2007-08-15 14:28:22 +0000 | [diff] [blame] | 380 | |
Georg Brandl | 952aea2 | 2007-09-04 17:50:40 +0000 | [diff] [blame] | 381 | Note that ``filter(function, iterable)`` is equivalent to the generator |
| 382 | expression ``(item for item in iterable if function(item))`` if function is |
| 383 | not ``None`` and ``(item for item in iterable if item)`` if function is |
| 384 | ``None``. |
Georg Brandl | 116aa62 | 2007-08-15 14:28:22 +0000 | [diff] [blame] | 385 | |
Raymond Hettinger | cdf8ba3 | 2009-02-19 04:45:07 +0000 | [diff] [blame] | 386 | See :func:`itertools.filterfalse` for the complementary function that returns |
| 387 | elements of *iterable* for which *function* returns false. |
| 388 | |
Georg Brandl | 116aa62 | 2007-08-15 14:28:22 +0000 | [diff] [blame] | 389 | |
| 390 | .. function:: float([x]) |
| 391 | |
Georg Brandl | 95817b3 | 2008-05-11 14:30:18 +0000 | [diff] [blame] | 392 | Convert a string or a number to floating point. If the argument is a string, |
| 393 | it must contain a possibly signed decimal or floating point number, possibly |
| 394 | embedded in whitespace. The argument may also be ``'[+|-]nan'`` or |
| 395 | ``'[+|-]inf'``. Otherwise, the argument may be an integer or a floating |
| 396 | point number, and a floating point number with the same value (within |
| 397 | Python's floating point precision) is returned. If no argument is given, |
| 398 | ``0.0`` is returned. |
Georg Brandl | 116aa62 | 2007-08-15 14:28:22 +0000 | [diff] [blame] | 399 | |
| 400 | .. note:: |
| 401 | |
| 402 | .. index:: |
| 403 | single: NaN |
| 404 | single: Infinity |
| 405 | |
Georg Brandl | 95817b3 | 2008-05-11 14:30:18 +0000 | [diff] [blame] | 406 | When passing in a string, values for NaN and Infinity may be returned, |
| 407 | depending on the underlying C library. Float accepts the strings |
| 408 | ``'nan'``, ``'inf'`` and ``'-inf'`` for NaN and positive or negative |
| 409 | infinity. The case and a leading + are ignored as well as a leading - is |
| 410 | ignored for NaN. Float always represents NaN and infinity as ``nan``, |
| 411 | ``inf`` or ``-inf``. |
Georg Brandl | 116aa62 | 2007-08-15 14:28:22 +0000 | [diff] [blame] | 412 | |
| 413 | The float type is described in :ref:`typesnumeric`. |
| 414 | |
Georg Brandl | 4b49131 | 2007-08-31 09:22:56 +0000 | [diff] [blame] | 415 | .. function:: format(value[, format_spec]) |
| 416 | |
| 417 | .. index:: |
| 418 | pair: str; format |
| 419 | single: __format__ |
Georg Brandl | 48310cd | 2009-01-03 21:18:54 +0000 | [diff] [blame] | 420 | |
Georg Brandl | 5579ba9 | 2009-02-23 10:24:05 +0000 | [diff] [blame] | 421 | Convert a *value* to a "formatted" representation, as controlled by |
| 422 | *format_spec*. The interpretation of *format_spec* will depend on the type |
| 423 | of the *value* argument, however there is a standard formatting syntax that |
| 424 | is used by most built-in types: :ref:`formatspec`. |
Georg Brandl | 48310cd | 2009-01-03 21:18:54 +0000 | [diff] [blame] | 425 | |
Georg Brandl | 4b49131 | 2007-08-31 09:22:56 +0000 | [diff] [blame] | 426 | .. note:: |
| 427 | |
Georg Brandl | 5579ba9 | 2009-02-23 10:24:05 +0000 | [diff] [blame] | 428 | ``format(value, format_spec)`` merely calls |
| 429 | ``value.__format__(format_spec)``. |
Georg Brandl | 4b49131 | 2007-08-31 09:22:56 +0000 | [diff] [blame] | 430 | |
| 431 | |
Georg Brandl | 116aa62 | 2007-08-15 14:28:22 +0000 | [diff] [blame] | 432 | .. function:: frozenset([iterable]) |
| 433 | :noindex: |
| 434 | |
| 435 | Return a frozenset object, optionally with elements taken from *iterable*. |
| 436 | The frozenset type is described in :ref:`types-set`. |
| 437 | |
| 438 | For other containers see the built in :class:`dict`, :class:`list`, and |
| 439 | :class:`tuple` classes, and the :mod:`collections` module. |
| 440 | |
Georg Brandl | 116aa62 | 2007-08-15 14:28:22 +0000 | [diff] [blame] | 441 | |
| 442 | .. function:: getattr(object, name[, default]) |
| 443 | |
| 444 | Return the value of the named attributed of *object*. *name* must be a string. |
| 445 | If the string is the name of one of the object's attributes, the result is the |
| 446 | value of that attribute. For example, ``getattr(x, 'foobar')`` is equivalent to |
| 447 | ``x.foobar``. If the named attribute does not exist, *default* is returned if |
| 448 | provided, otherwise :exc:`AttributeError` is raised. |
| 449 | |
| 450 | |
| 451 | .. function:: globals() |
| 452 | |
| 453 | Return a dictionary representing the current global symbol table. This is always |
| 454 | the dictionary of the current module (inside a function or method, this is the |
| 455 | module where it is defined, not the module from which it is called). |
| 456 | |
| 457 | |
| 458 | .. function:: hasattr(object, name) |
| 459 | |
| 460 | The arguments are an object and a string. The result is ``True`` if the string |
| 461 | is the name of one of the object's attributes, ``False`` if not. (This is |
| 462 | implemented by calling ``getattr(object, name)`` and seeing whether it raises an |
| 463 | exception or not.) |
| 464 | |
| 465 | |
| 466 | .. function:: hash(object) |
| 467 | |
| 468 | Return the hash value of the object (if it has one). Hash values are integers. |
| 469 | They are used to quickly compare dictionary keys during a dictionary lookup. |
| 470 | Numeric values that compare equal have the same hash value (even if they are of |
| 471 | different types, as is the case for 1 and 1.0). |
| 472 | |
| 473 | |
| 474 | .. function:: help([object]) |
| 475 | |
| 476 | Invoke the built-in help system. (This function is intended for interactive |
| 477 | use.) If no argument is given, the interactive help system starts on the |
| 478 | interpreter console. If the argument is a string, then the string is looked up |
| 479 | as the name of a module, function, class, method, keyword, or documentation |
| 480 | topic, and a help page is printed on the console. If the argument is any other |
| 481 | kind of object, a help page on the object is generated. |
| 482 | |
Christian Heimes | 9bd667a | 2008-01-20 15:14:11 +0000 | [diff] [blame] | 483 | This function is added to the built-in namespace by the :mod:`site` module. |
| 484 | |
Georg Brandl | 116aa62 | 2007-08-15 14:28:22 +0000 | [diff] [blame] | 485 | |
| 486 | .. function:: hex(x) |
| 487 | |
| 488 | Convert an integer number to a hexadecimal string. The result is a valid Python |
| 489 | expression. If *x* is not a Python :class:`int` object, it has to define an |
| 490 | :meth:`__index__` method that returns an integer. |
| 491 | |
Georg Brandl | 116aa62 | 2007-08-15 14:28:22 +0000 | [diff] [blame] | 492 | |
| 493 | .. function:: id(object) |
| 494 | |
Georg Brandl | ba956ae | 2007-11-29 17:24:34 +0000 | [diff] [blame] | 495 | Return the "identity" of an object. This is an integer which |
Georg Brandl | 116aa62 | 2007-08-15 14:28:22 +0000 | [diff] [blame] | 496 | is guaranteed to be unique and constant for this object during its lifetime. |
| 497 | Two objects with non-overlapping lifetimes may have the same :func:`id` value. |
| 498 | (Implementation note: this is the address of the object.) |
| 499 | |
| 500 | |
Georg Brandl | c090298 | 2007-09-12 21:29:27 +0000 | [diff] [blame] | 501 | .. function:: input([prompt]) |
| 502 | |
| 503 | If the *prompt* argument is present, it is written to standard output without |
| 504 | a trailing newline. The function then reads a line from input, converts it |
| 505 | to a string (stripping a trailing newline), and returns that. When EOF is |
| 506 | read, :exc:`EOFError` is raised. Example:: |
| 507 | |
Georg Brandl | 7b46942 | 2007-09-12 21:32:27 +0000 | [diff] [blame] | 508 | >>> s = input('--> ') |
Georg Brandl | c090298 | 2007-09-12 21:29:27 +0000 | [diff] [blame] | 509 | --> Monty Python's Flying Circus |
| 510 | >>> s |
| 511 | "Monty Python's Flying Circus" |
| 512 | |
Georg Brandl | 7b46942 | 2007-09-12 21:32:27 +0000 | [diff] [blame] | 513 | 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] | 514 | to provide elaborate line editing and history features. |
| 515 | |
| 516 | |
Georg Brandl | 225d3c8 | 2008-04-09 18:45:14 +0000 | [diff] [blame] | 517 | .. function:: int([number | string[, radix]]) |
Georg Brandl | 116aa62 | 2007-08-15 14:28:22 +0000 | [diff] [blame] | 518 | |
Georg Brandl | 225d3c8 | 2008-04-09 18:45:14 +0000 | [diff] [blame] | 519 | Convert a number or string to an integer. If no arguments are given, return |
| 520 | ``0``. If a number is given, return ``number.__int__()``. Conversion of |
| 521 | floating point numbers to integers truncates towards zero. A string must be |
| 522 | a base-radix integer literal optionally preceded by '+' or '-' (with no space |
| 523 | in between) and optionally surrounded by whitespace. A base-n literal |
| 524 | consists of the digits 0 to n-1, with 'a' to 'z' (or 'A' to 'Z') having |
| 525 | values 10 to 35. The default radix is 10. The allowed values are 0 and 2-36. |
| 526 | Base-2, -8, and -16 literals can be optionally prefixed with ``0b``/``0B``, |
| 527 | ``0o``/``0O``, or ``0x``/``0X``, as with integer literals in code. Radix 0 |
| 528 | means to interpret exactly as a code literal, so that the actual radix is 2, |
| 529 | 8, 10, or 16, and so that ``int('010', 0)`` is not legal, while |
| 530 | ``int('010')`` is, as well as ``int('010', 8)``. |
Georg Brandl | 116aa62 | 2007-08-15 14:28:22 +0000 | [diff] [blame] | 531 | |
| 532 | The integer type is described in :ref:`typesnumeric`. |
| 533 | |
| 534 | |
| 535 | .. function:: isinstance(object, classinfo) |
| 536 | |
Georg Brandl | 85eb8c1 | 2007-08-31 16:33:38 +0000 | [diff] [blame] | 537 | Return true if the *object* argument is an instance of the *classinfo* |
| 538 | argument, or of a (direct or indirect) subclass thereof. If *object* is not |
| 539 | an object of the given type, the function always returns false. If |
| 540 | *classinfo* is not a class (type object), it may be a tuple of type objects, |
| 541 | or may recursively contain other such tuples (other sequence types are not |
| 542 | accepted). If *classinfo* is not a type or tuple of types and such tuples, |
| 543 | a :exc:`TypeError` exception is raised. |
Georg Brandl | 116aa62 | 2007-08-15 14:28:22 +0000 | [diff] [blame] | 544 | |
Georg Brandl | 116aa62 | 2007-08-15 14:28:22 +0000 | [diff] [blame] | 545 | |
| 546 | .. function:: issubclass(class, classinfo) |
| 547 | |
| 548 | Return true if *class* is a subclass (direct or indirect) of *classinfo*. A |
| 549 | class is considered a subclass of itself. *classinfo* may be a tuple of class |
| 550 | objects, in which case every entry in *classinfo* will be checked. In any other |
| 551 | case, a :exc:`TypeError` exception is raised. |
| 552 | |
Georg Brandl | 116aa62 | 2007-08-15 14:28:22 +0000 | [diff] [blame] | 553 | |
Georg Brandl | 036490d | 2009-05-17 13:00:36 +0000 | [diff] [blame] | 554 | .. function:: iter(object[, sentinel]) |
Georg Brandl | 116aa62 | 2007-08-15 14:28:22 +0000 | [diff] [blame] | 555 | |
Georg Brandl | 036490d | 2009-05-17 13:00:36 +0000 | [diff] [blame] | 556 | Return an :term:`iterator` object. The first argument is interpreted very |
| 557 | differently depending on the presence of the second argument. Without a |
| 558 | second argument, *object* must be a collection object which supports the |
| 559 | iteration protocol (the :meth:`__iter__` method), or it must support the |
| 560 | sequence protocol (the :meth:`__getitem__` method with integer arguments |
| 561 | starting at ``0``). If it does not support either of those protocols, |
| 562 | :exc:`TypeError` is raised. If the second argument, *sentinel*, is given, |
| 563 | then *object* must be a callable object. The iterator created in this case |
| 564 | will call *object* with no arguments for each call to its :meth:`__next__` |
| 565 | method; if the value returned is equal to *sentinel*, :exc:`StopIteration` |
| 566 | will be raised, otherwise the value will be returned. |
Georg Brandl | 116aa62 | 2007-08-15 14:28:22 +0000 | [diff] [blame] | 567 | |
Benjamin Peterson | f07d002 | 2009-03-21 17:31:58 +0000 | [diff] [blame] | 568 | One useful application of the second form of :func:`iter` is to read lines of |
| 569 | a file until a certain line is reached. The following example reads a file |
| 570 | until ``"STOP"`` is reached: :: |
| 571 | |
| 572 | with open("mydata.txt") as fp: |
| 573 | for line in iter(fp.readline, "STOP"): |
| 574 | process_line(line) |
| 575 | |
Georg Brandl | 116aa62 | 2007-08-15 14:28:22 +0000 | [diff] [blame] | 576 | |
| 577 | .. function:: len(s) |
| 578 | |
| 579 | Return the length (the number of items) of an object. The argument may be a |
| 580 | sequence (string, tuple or list) or a mapping (dictionary). |
| 581 | |
| 582 | |
| 583 | .. function:: list([iterable]) |
| 584 | |
| 585 | Return a list whose items are the same and in the same order as *iterable*'s |
| 586 | items. *iterable* may be either a sequence, a container that supports |
| 587 | iteration, or an iterator object. If *iterable* is already a list, a copy is |
| 588 | made and returned, similar to ``iterable[:]``. For instance, ``list('abc')`` |
Georg Brandl | 036490d | 2009-05-17 13:00:36 +0000 | [diff] [blame] | 589 | returns ``['a', 'b', 'c']`` and ``list( (1, 2, 3) )`` returns ``[1, 2, 3]``. |
| 590 | If no argument is given, returns a new empty list, ``[]``. |
Georg Brandl | 116aa62 | 2007-08-15 14:28:22 +0000 | [diff] [blame] | 591 | |
Georg Brandl | 48310cd | 2009-01-03 21:18:54 +0000 | [diff] [blame] | 592 | :class:`list` is a mutable sequence type, as documented in :ref:`typesseq`. |
Georg Brandl | 116aa62 | 2007-08-15 14:28:22 +0000 | [diff] [blame] | 593 | |
Georg Brandl | 036490d | 2009-05-17 13:00:36 +0000 | [diff] [blame] | 594 | |
Georg Brandl | 116aa62 | 2007-08-15 14:28:22 +0000 | [diff] [blame] | 595 | .. function:: locals() |
| 596 | |
| 597 | Update and return a dictionary representing the current local symbol table. |
| 598 | |
Georg Brandl | e720c0a | 2009-04-27 16:20:50 +0000 | [diff] [blame] | 599 | .. note:: |
Georg Brandl | 116aa62 | 2007-08-15 14:28:22 +0000 | [diff] [blame] | 600 | |
Georg Brandl | 036490d | 2009-05-17 13:00:36 +0000 | [diff] [blame] | 601 | The contents of this dictionary should not be modified; changes may not |
| 602 | affect the values of local variables used by the interpreter. |
Georg Brandl | 116aa62 | 2007-08-15 14:28:22 +0000 | [diff] [blame] | 603 | |
Georg Brandl | 036490d | 2009-05-17 13:00:36 +0000 | [diff] [blame] | 604 | Free variables are returned by :func:`locals` when it is called in a function |
| 605 | block. Modifications of free variables may not affect the values used by the |
Georg Brandl | 116aa62 | 2007-08-15 14:28:22 +0000 | [diff] [blame] | 606 | interpreter. Free variables are not returned in class blocks. |
| 607 | |
| 608 | |
| 609 | .. function:: map(function, iterable, ...) |
| 610 | |
Georg Brandl | 952aea2 | 2007-09-04 17:50:40 +0000 | [diff] [blame] | 611 | Return an iterator that applies *function* to every item of *iterable*, |
| 612 | yielding the results. If additional *iterable* arguments are passed, |
| 613 | *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] | 614 | iterables in parallel. With multiple iterables, the iterator stops when the |
Raymond Hettinger | cdf8ba3 | 2009-02-19 04:45:07 +0000 | [diff] [blame] | 615 | shortest iterable is exhausted. For cases where the function inputs are |
| 616 | already arranged into argument tuples, see :func:`itertools.starmap`\. |
Georg Brandl | de2b00e | 2008-05-05 21:04:12 +0000 | [diff] [blame] | 617 | |
Georg Brandl | 116aa62 | 2007-08-15 14:28:22 +0000 | [diff] [blame] | 618 | |
Georg Brandl | 55ac8f0 | 2007-09-01 13:51:09 +0000 | [diff] [blame] | 619 | .. function:: max(iterable[, args...], *[, key]) |
Georg Brandl | 116aa62 | 2007-08-15 14:28:22 +0000 | [diff] [blame] | 620 | |
| 621 | With a single argument *iterable*, return the largest item of a non-empty |
| 622 | iterable (such as a string, tuple or list). With more than one argument, return |
| 623 | the largest of the arguments. |
| 624 | |
Georg Brandl | 55ac8f0 | 2007-09-01 13:51:09 +0000 | [diff] [blame] | 625 | The optional keyword-only *key* argument specifies a one-argument ordering |
| 626 | function like that used for :meth:`list.sort`. |
Georg Brandl | 116aa62 | 2007-08-15 14:28:22 +0000 | [diff] [blame] | 627 | |
| 628 | |
Georg Brandl | 85eb8c1 | 2007-08-31 16:33:38 +0000 | [diff] [blame] | 629 | .. function:: memoryview(obj) |
Benjamin Peterson | 6dfcb02 | 2008-09-10 21:02:02 +0000 | [diff] [blame] | 630 | :noindex: |
Georg Brandl | 85eb8c1 | 2007-08-31 16:33:38 +0000 | [diff] [blame] | 631 | |
Benjamin Peterson | 1b25b92 | 2008-09-09 22:15:27 +0000 | [diff] [blame] | 632 | Return a "memory view" object created from the given argument. See |
| 633 | :ref:`typememoryview` for more information. |
Georg Brandl | 85eb8c1 | 2007-08-31 16:33:38 +0000 | [diff] [blame] | 634 | |
| 635 | |
Georg Brandl | 55ac8f0 | 2007-09-01 13:51:09 +0000 | [diff] [blame] | 636 | .. function:: min(iterable[, args...], *[, key]) |
Georg Brandl | 116aa62 | 2007-08-15 14:28:22 +0000 | [diff] [blame] | 637 | |
| 638 | With a single argument *iterable*, return the smallest item of a non-empty |
| 639 | iterable (such as a string, tuple or list). With more than one argument, return |
| 640 | the smallest of the arguments. |
| 641 | |
Georg Brandl | 55ac8f0 | 2007-09-01 13:51:09 +0000 | [diff] [blame] | 642 | The optional keyword-only *key* argument specifies a one-argument ordering |
| 643 | function like that used for :meth:`list.sort`. |
Georg Brandl | 116aa62 | 2007-08-15 14:28:22 +0000 | [diff] [blame] | 644 | |
| 645 | |
| 646 | .. function:: next(iterator[, default]) |
| 647 | |
Georg Brandl | c14bb75 | 2008-04-29 21:00:18 +0000 | [diff] [blame] | 648 | Retrieve the next item from the *iterator* by calling its :meth:`__next__` |
Georg Brandl | 116aa62 | 2007-08-15 14:28:22 +0000 | [diff] [blame] | 649 | method. If *default* is given, it is returned if the iterator is exhausted, |
| 650 | otherwise :exc:`StopIteration` is raised. |
| 651 | |
| 652 | |
| 653 | .. function:: object() |
| 654 | |
Georg Brandl | 85eb8c1 | 2007-08-31 16:33:38 +0000 | [diff] [blame] | 655 | 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] | 656 | It has the methods that are common to all instances of Python classes. This |
| 657 | function does not accept any arguments. |
Georg Brandl | 85eb8c1 | 2007-08-31 16:33:38 +0000 | [diff] [blame] | 658 | |
| 659 | .. note:: |
| 660 | |
| 661 | :class:`object` does *not* have a :attr:`__dict__`, so you can't assign |
| 662 | arbitrary attributes to an instance of the :class:`object` class. |
Georg Brandl | 116aa62 | 2007-08-15 14:28:22 +0000 | [diff] [blame] | 663 | |
Georg Brandl | 116aa62 | 2007-08-15 14:28:22 +0000 | [diff] [blame] | 664 | |
| 665 | .. function:: oct(x) |
| 666 | |
| 667 | Convert an integer number to an octal string. The result is a valid Python |
| 668 | expression. If *x* is not a Python :class:`int` object, it has to define an |
| 669 | :meth:`__index__` method that returns an integer. |
| 670 | |
Georg Brandl | 116aa62 | 2007-08-15 14:28:22 +0000 | [diff] [blame] | 671 | |
Georg Brandl | 036490d | 2009-05-17 13:00:36 +0000 | [diff] [blame] | 672 | .. function:: open(file, mode='r', buffering=None, encoding=None, errors=None, newline=None, closefd=True) |
Georg Brandl | 116aa62 | 2007-08-15 14:28:22 +0000 | [diff] [blame] | 673 | |
Benjamin Peterson | 52c3bf1 | 2009-03-23 02:44:58 +0000 | [diff] [blame] | 674 | Open *file* and return a corresponding stream. If the file cannot be opened, |
| 675 | an :exc:`IOError` is raised. |
Georg Brandl | 48310cd | 2009-01-03 21:18:54 +0000 | [diff] [blame] | 676 | |
Georg Brandl | 76e5538 | 2008-10-08 16:34:57 +0000 | [diff] [blame] | 677 | *file* is either a string or bytes object giving the name (and the path if |
| 678 | the file isn't in the current working directory) of the file to be opened or |
| 679 | an integer file descriptor of the file to be wrapped. (If a file descriptor |
| 680 | is given, it is closed when the returned I/O object is closed, unless |
| 681 | *closefd* is set to ``False``.) |
Georg Brandl | 116aa62 | 2007-08-15 14:28:22 +0000 | [diff] [blame] | 682 | |
Mark Summerfield | ecff60e | 2007-12-14 10:07:44 +0000 | [diff] [blame] | 683 | *mode* is an optional string that specifies the mode in which the file is |
Georg Brandl | 7b6ca4a | 2009-04-27 06:13:55 +0000 | [diff] [blame] | 684 | opened. The available modes are: |
Georg Brandl | 116aa62 | 2007-08-15 14:28:22 +0000 | [diff] [blame] | 685 | |
Benjamin Peterson | dd21912 | 2008-04-11 21:17:32 +0000 | [diff] [blame] | 686 | ========= =============================================================== |
| 687 | Character Meaning |
| 688 | --------- --------------------------------------------------------------- |
| 689 | ``'r'`` open for reading (default) |
Georg Brandl | 7b6ca4a | 2009-04-27 06:13:55 +0000 | [diff] [blame] | 690 | ``'w'`` open for writing, truncating the file first if it exists |
Benjamin Peterson | dd21912 | 2008-04-11 21:17:32 +0000 | [diff] [blame] | 691 | ``'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] | 692 | ========= =============================================================== |
| 693 | |
| 694 | Several characters can be appended that modify the given mode: |
| 695 | |
| 696 | ========= =============================================================== |
Benjamin Peterson | dd21912 | 2008-04-11 21:17:32 +0000 | [diff] [blame] | 697 | ``'t'`` text mode (default) |
Georg Brandl | 7b6ca4a | 2009-04-27 06:13:55 +0000 | [diff] [blame] | 698 | ``'b'`` binary mode |
| 699 | ``'+'`` open for updating (reading and writing) |
Benjamin Peterson | 52c3bf1 | 2009-03-23 02:44:58 +0000 | [diff] [blame] | 700 | ``'U'`` universal newline mode (for backwards compatibility; should |
| 701 | not be used in new code) |
Benjamin Peterson | dd21912 | 2008-04-11 21:17:32 +0000 | [diff] [blame] | 702 | ========= =============================================================== |
Mark Summerfield | ecff60e | 2007-12-14 10:07:44 +0000 | [diff] [blame] | 703 | |
Georg Brandl | 7b6ca4a | 2009-04-27 06:13:55 +0000 | [diff] [blame] | 704 | The mode ``'w+'`` opens and truncates the file to 0 bytes, while ``'r+'`` |
| 705 | opens the file without truncation. On *some* Unix systems, append mode means |
| 706 | that *all* writes append to the end of the file regardless of the current |
| 707 | seek position. |
Skip Montanaro | 1c63960 | 2007-09-23 19:49:54 +0000 | [diff] [blame] | 708 | |
Benjamin Peterson | 52c3bf1 | 2009-03-23 02:44:58 +0000 | [diff] [blame] | 709 | Python distinguishes between files opened in binary and text modes, even when |
| 710 | the underlying operating system doesn't. Files opened in binary mode |
| 711 | (including ``'b'`` in the *mode* argument) return contents as ``bytes`` |
| 712 | objects without any decoding. In text mode (the default, or when ``'t'`` is |
| 713 | included in the *mode* argument), the contents of the file are returned as |
Georg Brandl | 7b6ca4a | 2009-04-27 06:13:55 +0000 | [diff] [blame] | 714 | strings, the bytes having been first decoded using the specified *encoding*. |
| 715 | If *encoding* is not specified, a platform-dependent default encoding is |
| 716 | used, see below. |
Mark Summerfield | ecff60e | 2007-12-14 10:07:44 +0000 | [diff] [blame] | 717 | |
Benjamin Peterson | dd21912 | 2008-04-11 21:17:32 +0000 | [diff] [blame] | 718 | *buffering* is an optional integer used to set the buffering policy. By |
Benjamin Peterson | 52c3bf1 | 2009-03-23 02:44:58 +0000 | [diff] [blame] | 719 | default full buffering is on. Pass 0 to switch buffering off (only allowed |
| 720 | in binary mode), 1 to set line buffering, and an integer > 1 for full |
| 721 | buffering. |
Georg Brandl | 48310cd | 2009-01-03 21:18:54 +0000 | [diff] [blame] | 722 | |
Benjamin Peterson | dd21912 | 2008-04-11 21:17:32 +0000 | [diff] [blame] | 723 | *encoding* is the name of the encoding used to decode or encode the file. |
| 724 | 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] | 725 | dependent (whatever :func:`locale.getpreferredencoding` returns), but any |
| 726 | encoding supported by Python can be used. See the :mod:`codecs` module for |
| 727 | the list of supported encodings. |
Mark Summerfield | ecff60e | 2007-12-14 10:07:44 +0000 | [diff] [blame] | 728 | |
Benjamin Peterson | 52c3bf1 | 2009-03-23 02:44:58 +0000 | [diff] [blame] | 729 | *errors* is an optional string that specifies how encoding and decoding |
| 730 | errors are to be handled--this cannot be used in binary mode. Pass |
| 731 | ``'strict'`` to raise a :exc:`ValueError` exception if there is an encoding |
| 732 | error (the default of ``None`` has the same effect), or pass ``'ignore'`` to |
| 733 | ignore errors. (Note that ignoring encoding errors can lead to data loss.) |
| 734 | ``'replace'`` causes a replacement marker (such as ``'?'``) to be inserted |
| 735 | where there is malformed data. When writing, ``'xmlcharrefreplace'`` |
| 736 | (replace with the appropriate XML character reference) or |
| 737 | ``'backslashreplace'`` (replace with backslashed escape sequences) can be |
| 738 | used. Any other error handling name that has been registered with |
| 739 | :func:`codecs.register_error` is also valid. |
Mark Summerfield | ecff60e | 2007-12-14 10:07:44 +0000 | [diff] [blame] | 740 | |
Benjamin Peterson | dd21912 | 2008-04-11 21:17:32 +0000 | [diff] [blame] | 741 | *newline* controls how universal newlines works (it only applies to text |
| 742 | mode). It can be ``None``, ``''``, ``'\n'``, ``'\r'``, and ``'\r\n'``. It |
| 743 | works as follows: |
Mark Summerfield | ecff60e | 2007-12-14 10:07:44 +0000 | [diff] [blame] | 744 | |
Benjamin Peterson | dd21912 | 2008-04-11 21:17:32 +0000 | [diff] [blame] | 745 | * On input, if *newline* is ``None``, universal newlines mode is enabled. |
| 746 | Lines in the input can end in ``'\n'``, ``'\r'``, or ``'\r\n'``, and these |
| 747 | are translated into ``'\n'`` before being returned to the caller. If it is |
| 748 | ``''``, universal newline mode is enabled, but line endings are returned to |
| 749 | the caller untranslated. If it has any of the other legal values, input |
| 750 | lines are only terminated by the given string, and the line ending is |
| 751 | returned to the caller untranslated. |
| 752 | |
| 753 | * On output, if *newline* is ``None``, any ``'\n'`` characters written are |
| 754 | translated to the system default line separator, :data:`os.linesep`. If |
| 755 | *newline* is ``''``, no translation takes place. If *newline* is any of |
| 756 | the other legal values, any ``'\n'`` characters written are translated to |
| 757 | the given string. |
| 758 | |
Benjamin Peterson | 8cad9c7 | 2009-03-23 02:38:01 +0000 | [diff] [blame] | 759 | If *closefd* is ``False`` and a file descriptor rather than a filename was |
| 760 | given, the underlying file descriptor will be kept open when the file is |
| 761 | closed. If a filename is given *closefd* has no effect and must be ``True`` |
| 762 | (the default). |
| 763 | |
| 764 | The type of file object returned by the :func:`open` function depends on the |
| 765 | mode. When :func:`open` is used to open a file in a text mode (``'w'``, |
| 766 | ``'r'``, ``'wt'``, ``'rt'``, etc.), it returns a subclass of |
| 767 | :class:`io.TextIOBase` (specifically :class:`io.TextIOWrapper`). When used |
| 768 | to open a file in a binary mode with buffering, the returned class is a |
| 769 | subclass of :class:`io.BufferedIOBase`. The exact class varies: in read |
| 770 | binary mode, it returns a :class:`io.BufferedReader`; in write binary and |
| 771 | append binary modes, it returns a :class:`io.BufferedWriter`, and in |
| 772 | read/write mode, it returns a :class:`io.BufferedRandom`. When buffering is |
| 773 | disabled, the raw stream, a subclass of :class:`io.RawIOBase`, |
| 774 | :class:`io.FileIO`, is returned. |
Georg Brandl | 116aa62 | 2007-08-15 14:28:22 +0000 | [diff] [blame] | 775 | |
| 776 | .. index:: |
| 777 | single: line-buffered I/O |
| 778 | single: unbuffered I/O |
| 779 | single: buffer size, I/O |
| 780 | single: I/O control; buffering |
Skip Montanaro | 4d8c193 | 2007-09-23 21:13:45 +0000 | [diff] [blame] | 781 | single: binary mode |
| 782 | single: text mode |
| 783 | module: sys |
Georg Brandl | 116aa62 | 2007-08-15 14:28:22 +0000 | [diff] [blame] | 784 | |
Benjamin Peterson | dd21912 | 2008-04-11 21:17:32 +0000 | [diff] [blame] | 785 | See also the file handling modules, such as, :mod:`fileinput`, :mod:`io` |
Benjamin Peterson | 8cad9c7 | 2009-03-23 02:38:01 +0000 | [diff] [blame] | 786 | (where :func:`open` is declared), :mod:`os`, :mod:`os.path`, :mod:`tempfile`, |
| 787 | and :mod:`shutil`. |
Georg Brandl | 116aa62 | 2007-08-15 14:28:22 +0000 | [diff] [blame] | 788 | |
Georg Brandl | f694518 | 2008-02-01 11:56:49 +0000 | [diff] [blame] | 789 | |
| 790 | .. XXX works for bytes too, but should it? |
Georg Brandl | 116aa62 | 2007-08-15 14:28:22 +0000 | [diff] [blame] | 791 | .. function:: ord(c) |
| 792 | |
| 793 | Given a string of length one, return an integer representing the Unicode code |
Georg Brandl | f694518 | 2008-02-01 11:56:49 +0000 | [diff] [blame] | 794 | point of the character. For example, ``ord('a')`` returns the integer ``97`` |
| 795 | and ``ord('\u2020')`` returns ``8224``. This is the inverse of :func:`chr`. |
| 796 | |
| 797 | If the argument length is not one, a :exc:`TypeError` will be raised. (If |
| 798 | Python was built with UCS2 Unicode, then the character's code point must be |
| 799 | in the range [0..65535] inclusive; otherwise the string length is two!) |
Georg Brandl | 116aa62 | 2007-08-15 14:28:22 +0000 | [diff] [blame] | 800 | |
| 801 | |
| 802 | .. function:: pow(x, y[, z]) |
| 803 | |
| 804 | Return *x* to the power *y*; if *z* is present, return *x* to the power *y*, |
| 805 | modulo *z* (computed more efficiently than ``pow(x, y) % z``). The two-argument |
| 806 | form ``pow(x, y)`` is equivalent to using the power operator: ``x**y``. |
| 807 | |
Georg Brandl | e06de8b | 2008-05-05 21:42:51 +0000 | [diff] [blame] | 808 | The arguments must have numeric types. With mixed operand types, the |
| 809 | coercion rules for binary arithmetic operators apply. For :class:`int` |
| 810 | operands, the result has the same type as the operands (after coercion) |
| 811 | unless the second argument is negative; in that case, all arguments are |
| 812 | converted to float and a float result is delivered. For example, ``10**2`` |
| 813 | returns ``100``, but ``10**-2`` returns ``0.01``. If the second argument is |
| 814 | negative, the third argument must be omitted. If *z* is present, *x* and *y* |
| 815 | must be of integer types, and *y* must be non-negative. |
Georg Brandl | 116aa62 | 2007-08-15 14:28:22 +0000 | [diff] [blame] | 816 | |
| 817 | |
Georg Brandl | 036490d | 2009-05-17 13:00:36 +0000 | [diff] [blame] | 818 | .. function:: print([object, ...], *, sep=' ', end='\\n', file=sys.stdout) |
Georg Brandl | f694518 | 2008-02-01 11:56:49 +0000 | [diff] [blame] | 819 | |
| 820 | Print *object*\(s) to the stream *file*, separated by *sep* and followed by |
| 821 | *end*. *sep*, *end* and *file*, if present, must be given as keyword |
| 822 | arguments. |
| 823 | |
| 824 | All non-keyword arguments are converted to strings like :func:`str` does and |
| 825 | written to the stream, separated by *sep* and followed by *end*. Both *sep* |
| 826 | and *end* must be strings; they can also be ``None``, which means to use the |
| 827 | default values. If no *object* is given, :func:`print` will just write |
| 828 | *end*. |
| 829 | |
| 830 | The *file* argument must be an object with a ``write(string)`` method; if it |
| 831 | is not present or ``None``, :data:`sys.stdout` will be used. |
| 832 | |
| 833 | |
Georg Brandl | 036490d | 2009-05-17 13:00:36 +0000 | [diff] [blame] | 834 | .. function:: property(fget=None, fset=None, fdel=None, doc=None) |
Georg Brandl | 116aa62 | 2007-08-15 14:28:22 +0000 | [diff] [blame] | 835 | |
Georg Brandl | 85eb8c1 | 2007-08-31 16:33:38 +0000 | [diff] [blame] | 836 | Return a property attribute. |
Georg Brandl | 116aa62 | 2007-08-15 14:28:22 +0000 | [diff] [blame] | 837 | |
| 838 | *fget* is a function for getting an attribute value, likewise *fset* is a |
| 839 | function for setting, and *fdel* a function for del'ing, an attribute. Typical |
| 840 | use is to define a managed attribute x:: |
| 841 | |
| 842 | class C(object): |
Alexandre Vassalotti | 5f8ced2 | 2008-05-16 00:03:33 +0000 | [diff] [blame] | 843 | def __init__(self): |
| 844 | self._x = None |
| 845 | |
| 846 | def getx(self): |
| 847 | return self._x |
| 848 | def setx(self, value): |
| 849 | self._x = value |
| 850 | def delx(self): |
| 851 | del self._x |
Georg Brandl | 116aa62 | 2007-08-15 14:28:22 +0000 | [diff] [blame] | 852 | x = property(getx, setx, delx, "I'm the 'x' property.") |
| 853 | |
| 854 | If given, *doc* will be the docstring of the property attribute. Otherwise, the |
| 855 | 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] | 856 | create read-only properties easily using :func:`property` as a :term:`decorator`:: |
Georg Brandl | 116aa62 | 2007-08-15 14:28:22 +0000 | [diff] [blame] | 857 | |
| 858 | class Parrot(object): |
| 859 | def __init__(self): |
| 860 | self._voltage = 100000 |
| 861 | |
| 862 | @property |
| 863 | def voltage(self): |
| 864 | """Get the current voltage.""" |
| 865 | return self._voltage |
| 866 | |
Alexandre Vassalotti | 5f8ced2 | 2008-05-16 00:03:33 +0000 | [diff] [blame] | 867 | turns the :meth:`voltage` method into a "getter" for a read-only attribute |
| 868 | with the same name. |
| 869 | |
| 870 | A property object has :attr:`getter`, :attr:`setter`, and :attr:`deleter` |
| 871 | methods usable as decorators that create a copy of the property with the |
| 872 | corresponding accessor function set to the decorated function. This is |
| 873 | best explained with an example:: |
| 874 | |
| 875 | class C(object): |
Benjamin Peterson | 206e307 | 2008-10-19 14:07:49 +0000 | [diff] [blame] | 876 | def __init__(self): |
| 877 | self._x = None |
Alexandre Vassalotti | 5f8ced2 | 2008-05-16 00:03:33 +0000 | [diff] [blame] | 878 | |
| 879 | @property |
| 880 | def x(self): |
| 881 | """I'm the 'x' property.""" |
| 882 | return self._x |
| 883 | |
| 884 | @x.setter |
| 885 | def x(self, value): |
| 886 | self._x = value |
| 887 | |
| 888 | @x.deleter |
| 889 | def x(self): |
| 890 | del self._x |
| 891 | |
| 892 | This code is exactly equivalent to the first example. Be sure to give the |
| 893 | additional functions the same name as the original property (``x`` in this |
| 894 | case.) |
| 895 | |
| 896 | The returned property also has the attributes ``fget``, ``fset``, and |
| 897 | ``fdel`` corresponding to the constructor arguments. |
Georg Brandl | 116aa62 | 2007-08-15 14:28:22 +0000 | [diff] [blame] | 898 | |
Georg Brandl | 116aa62 | 2007-08-15 14:28:22 +0000 | [diff] [blame] | 899 | |
Georg Brandl | 952aea2 | 2007-09-04 17:50:40 +0000 | [diff] [blame] | 900 | .. XXX does accept objects with __index__ too |
Georg Brandl | 116aa62 | 2007-08-15 14:28:22 +0000 | [diff] [blame] | 901 | .. function:: range([start,] stop[, step]) |
| 902 | |
Georg Brandl | bf086a1 | 2008-05-12 16:53:56 +0000 | [diff] [blame] | 903 | This is a versatile function to create iterables yielding arithmetic |
Georg Brandl | 95817b3 | 2008-05-11 14:30:18 +0000 | [diff] [blame] | 904 | progressions. It is most often used in :keyword:`for` loops. The arguments |
| 905 | must be integers. If the *step* argument is omitted, it defaults to ``1``. |
| 906 | If the *start* argument is omitted, it defaults to ``0``. The full form |
Georg Brandl | bf086a1 | 2008-05-12 16:53:56 +0000 | [diff] [blame] | 907 | returns an iterable of integers ``[start, start + step, start + 2 * step, |
Georg Brandl | 95817b3 | 2008-05-11 14:30:18 +0000 | [diff] [blame] | 908 | ...]``. If *step* is positive, the last element is the largest ``start + i * |
| 909 | step`` less than *stop*; if *step* is negative, the last element is the |
| 910 | smallest ``start + i * step`` greater than *stop*. *step* must not be zero |
| 911 | (or else :exc:`ValueError` is raised). Example: |
Georg Brandl | 116aa62 | 2007-08-15 14:28:22 +0000 | [diff] [blame] | 912 | |
| 913 | >>> list(range(10)) |
| 914 | [0, 1, 2, 3, 4, 5, 6, 7, 8, 9] |
| 915 | >>> list(range(1, 11)) |
| 916 | [1, 2, 3, 4, 5, 6, 7, 8, 9, 10] |
| 917 | >>> list(range(0, 30, 5)) |
| 918 | [0, 5, 10, 15, 20, 25] |
| 919 | >>> list(range(0, 10, 3)) |
| 920 | [0, 3, 6, 9] |
| 921 | >>> list(range(0, -10, -1)) |
| 922 | [0, -1, -2, -3, -4, -5, -6, -7, -8, -9] |
| 923 | >>> list(range(0)) |
| 924 | [] |
| 925 | >>> list(range(1, 0)) |
| 926 | [] |
| 927 | |
| 928 | |
| 929 | .. function:: repr(object) |
| 930 | |
Georg Brandl | 68ee3a5 | 2008-03-25 07:21:32 +0000 | [diff] [blame] | 931 | Return a string containing a printable representation of an object. For many |
| 932 | types, this function makes an attempt to return a string that would yield an |
| 933 | object with the same value when passed to :func:`eval`, otherwise the |
| 934 | representation is a string enclosed in angle brackets that contains the name |
| 935 | of the type of the object together with additional information often |
| 936 | including the name and address of the object. A class can control what this |
| 937 | function returns for its instances by defining a :meth:`__repr__` method. |
Georg Brandl | 116aa62 | 2007-08-15 14:28:22 +0000 | [diff] [blame] | 938 | |
| 939 | |
| 940 | .. function:: reversed(seq) |
| 941 | |
Christian Heimes | 7f04431 | 2008-01-06 17:05:40 +0000 | [diff] [blame] | 942 | Return a reverse :term:`iterator`. *seq* must be an object which has |
| 943 | a :meth:`__reversed__` method or supports the sequence protocol (the |
| 944 | :meth:`__len__` method and the :meth:`__getitem__` method with integer |
| 945 | arguments starting at ``0``). |
Georg Brandl | 116aa62 | 2007-08-15 14:28:22 +0000 | [diff] [blame] | 946 | |
Georg Brandl | 116aa62 | 2007-08-15 14:28:22 +0000 | [diff] [blame] | 947 | |
| 948 | .. function:: round(x[, n]) |
| 949 | |
| 950 | Return the floating point value *x* rounded to *n* digits after the decimal |
Georg Brandl | 809ddaa | 2008-07-01 20:39:59 +0000 | [diff] [blame] | 951 | point. If *n* is omitted, it defaults to zero. Delegates to |
| 952 | ``x.__round__(n)``. |
| 953 | |
| 954 | For the built-in types supporting :func:`round`, values are rounded to the |
Christian Heimes | 072c0f1 | 2008-01-03 23:01:04 +0000 | [diff] [blame] | 955 | closest multiple of 10 to the power minus *n*; if two multiples are equally |
| 956 | close, rounding is done toward the even choice (so, for example, both |
Georg Brandl | 809ddaa | 2008-07-01 20:39:59 +0000 | [diff] [blame] | 957 | ``round(0.5)`` and ``round(-0.5)`` are ``0``, and ``round(1.5)`` is ``2``). |
| 958 | The return value is an integer if called with one argument, otherwise of the |
| 959 | same type as *x*. |
Christian Heimes | 072c0f1 | 2008-01-03 23:01:04 +0000 | [diff] [blame] | 960 | |
Georg Brandl | 116aa62 | 2007-08-15 14:28:22 +0000 | [diff] [blame] | 961 | |
| 962 | .. function:: set([iterable]) |
| 963 | :noindex: |
| 964 | |
| 965 | Return a new set, optionally with elements are taken from *iterable*. |
| 966 | The set type is described in :ref:`types-set`. |
| 967 | |
Georg Brandl | 116aa62 | 2007-08-15 14:28:22 +0000 | [diff] [blame] | 968 | |
| 969 | .. function:: setattr(object, name, value) |
| 970 | |
| 971 | This is the counterpart of :func:`getattr`. The arguments are an object, a |
| 972 | string and an arbitrary value. The string may name an existing attribute or a |
| 973 | new attribute. The function assigns the value to the attribute, provided the |
| 974 | object allows it. For example, ``setattr(x, 'foobar', 123)`` is equivalent to |
| 975 | ``x.foobar = 123``. |
| 976 | |
| 977 | |
| 978 | .. function:: slice([start,] stop[, step]) |
| 979 | |
| 980 | .. index:: single: Numerical Python |
| 981 | |
Christian Heimes | d8654cf | 2007-12-02 15:22:16 +0000 | [diff] [blame] | 982 | Return a :term:`slice` object representing the set of indices specified by |
Georg Brandl | 116aa62 | 2007-08-15 14:28:22 +0000 | [diff] [blame] | 983 | ``range(start, stop, step)``. The *start* and *step* arguments default to |
| 984 | ``None``. Slice objects have read-only data attributes :attr:`start`, |
| 985 | :attr:`stop` and :attr:`step` which merely return the argument values (or their |
| 986 | default). They have no other explicit functionality; however they are used by |
| 987 | Numerical Python and other third party extensions. Slice objects are also |
| 988 | generated when extended indexing syntax is used. For example: |
Raymond Hettinger | cdf8ba3 | 2009-02-19 04:45:07 +0000 | [diff] [blame] | 989 | ``a[start:stop:step]`` or ``a[start:stop, i]``. See :func:`itertools.islice` |
| 990 | for an alternate version that returns an iterator. |
Georg Brandl | 116aa62 | 2007-08-15 14:28:22 +0000 | [diff] [blame] | 991 | |
| 992 | |
Georg Brandl | 036490d | 2009-05-17 13:00:36 +0000 | [diff] [blame] | 993 | .. function:: sorted(iterable[, key][, reverse]) |
Georg Brandl | 116aa62 | 2007-08-15 14:28:22 +0000 | [diff] [blame] | 994 | |
| 995 | Return a new sorted list from the items in *iterable*. |
| 996 | |
Raymond Hettinger | 51b9c24 | 2008-02-14 13:52:24 +0000 | [diff] [blame] | 997 | Has two optional arguments which must be specified as keyword arguments. |
Georg Brandl | 116aa62 | 2007-08-15 14:28:22 +0000 | [diff] [blame] | 998 | |
Georg Brandl | 116aa62 | 2007-08-15 14:28:22 +0000 | [diff] [blame] | 999 | *key* specifies a function of one argument that is used to extract a comparison |
Christian Heimes | faf2f63 | 2008-01-06 16:59:19 +0000 | [diff] [blame] | 1000 | key from each list element: ``key=str.lower``. The default value is ``None``. |
Georg Brandl | 116aa62 | 2007-08-15 14:28:22 +0000 | [diff] [blame] | 1001 | |
| 1002 | *reverse* is a boolean value. If set to ``True``, then the list elements are |
| 1003 | sorted as if each comparison were reversed. |
| 1004 | |
Raymond Hettinger | 477be82 | 2009-02-19 06:44:30 +0000 | [diff] [blame] | 1005 | To convert an old-style *cmp* function to a *key* function, see the |
| 1006 | `CmpToKey recipe in the ASPN cookbook |
| 1007 | <http://code.activestate.com/recipes/576653/>`_\. |
Georg Brandl | 116aa62 | 2007-08-15 14:28:22 +0000 | [diff] [blame] | 1008 | |
| 1009 | .. function:: staticmethod(function) |
| 1010 | |
| 1011 | Return a static method for *function*. |
| 1012 | |
| 1013 | A static method does not receive an implicit first argument. To declare a static |
| 1014 | method, use this idiom:: |
| 1015 | |
| 1016 | class C: |
| 1017 | @staticmethod |
| 1018 | def f(arg1, arg2, ...): ... |
| 1019 | |
Christian Heimes | d8654cf | 2007-12-02 15:22:16 +0000 | [diff] [blame] | 1020 | The ``@staticmethod`` form is a function :term:`decorator` -- see the |
| 1021 | description of function definitions in :ref:`function` for details. |
Georg Brandl | 116aa62 | 2007-08-15 14:28:22 +0000 | [diff] [blame] | 1022 | |
| 1023 | It can be called either on the class (such as ``C.f()``) or on an instance (such |
| 1024 | as ``C().f()``). The instance is ignored except for its class. |
| 1025 | |
| 1026 | Static methods in Python are similar to those found in Java or C++. For a more |
| 1027 | advanced concept, see :func:`classmethod` in this section. |
| 1028 | |
| 1029 | For more information on static methods, consult the documentation on the |
| 1030 | standard type hierarchy in :ref:`types`. |
| 1031 | |
Georg Brandl | 116aa62 | 2007-08-15 14:28:22 +0000 | [diff] [blame] | 1032 | |
| 1033 | .. function:: str([object[, encoding[, errors]]]) |
| 1034 | |
| 1035 | Return a string version of an object, using one of the following modes: |
Georg Brandl | 48310cd | 2009-01-03 21:18:54 +0000 | [diff] [blame] | 1036 | |
Georg Brandl | 116aa62 | 2007-08-15 14:28:22 +0000 | [diff] [blame] | 1037 | If *encoding* and/or *errors* are given, :func:`str` will decode the |
| 1038 | *object* which can either be a byte string or a character buffer using |
| 1039 | the codec for *encoding*. The *encoding* parameter is a string giving |
| 1040 | the name of an encoding; if the encoding is not known, :exc:`LookupError` |
| 1041 | is raised. Error handling is done according to *errors*; this specifies the |
| 1042 | treatment of characters which are invalid in the input encoding. If |
| 1043 | *errors* is ``'strict'`` (the default), a :exc:`ValueError` is raised on |
| 1044 | errors, while a value of ``'ignore'`` causes errors to be silently ignored, |
| 1045 | and a value of ``'replace'`` causes the official Unicode replacement character, |
| 1046 | U+FFFD, to be used to replace input characters which cannot be decoded. |
Georg Brandl | 48310cd | 2009-01-03 21:18:54 +0000 | [diff] [blame] | 1047 | See also the :mod:`codecs` module. |
Georg Brandl | 116aa62 | 2007-08-15 14:28:22 +0000 | [diff] [blame] | 1048 | |
| 1049 | When only *object* is given, this returns its nicely printable representation. |
| 1050 | For strings, this is the string itself. The difference with ``repr(object)`` |
| 1051 | is that ``str(object)`` does not always attempt to return a string that is |
| 1052 | acceptable to :func:`eval`; its goal is to return a printable string. |
| 1053 | With no arguments, this returns the empty string. |
| 1054 | |
| 1055 | Objects can specify what ``str(object)`` returns by defining a :meth:`__str__` |
| 1056 | special method. |
| 1057 | |
| 1058 | For more information on strings see :ref:`typesseq` which describes sequence |
| 1059 | functionality (strings are sequences), and also the string-specific methods |
Georg Brandl | 4b49131 | 2007-08-31 09:22:56 +0000 | [diff] [blame] | 1060 | described in the :ref:`string-methods` section. To output formatted strings, |
| 1061 | see the :ref:`string-formatting` section. In addition see the |
| 1062 | :ref:`stringservices` section. |
Georg Brandl | 116aa62 | 2007-08-15 14:28:22 +0000 | [diff] [blame] | 1063 | |
| 1064 | |
| 1065 | .. function:: sum(iterable[, start]) |
| 1066 | |
| 1067 | Sums *start* and the items of an *iterable* from left to right and returns the |
| 1068 | total. *start* defaults to ``0``. The *iterable*'s items are normally numbers, |
| 1069 | and are not allowed to be strings. The fast, correct way to concatenate a |
Raymond Hettinger | cdf8ba3 | 2009-02-19 04:45:07 +0000 | [diff] [blame] | 1070 | sequence of strings is by calling ``''.join(sequence)``. To add floating |
| 1071 | point values with extended precision, see :func:`math.fsum`\. |
Georg Brandl | 116aa62 | 2007-08-15 14:28:22 +0000 | [diff] [blame] | 1072 | |
Georg Brandl | 116aa62 | 2007-08-15 14:28:22 +0000 | [diff] [blame] | 1073 | |
Mark Summerfield | 1041f74 | 2008-02-26 13:27:00 +0000 | [diff] [blame] | 1074 | .. function:: super([type[, object-or-type]]) |
Georg Brandl | 116aa62 | 2007-08-15 14:28:22 +0000 | [diff] [blame] | 1075 | |
Raymond Hettinger | 4d9a823 | 2009-02-24 23:30:43 +0000 | [diff] [blame] | 1076 | Return a proxy object that delegates method calls to a parent or sibling |
| 1077 | class of *type*. This is useful for accessing inherited methods that have |
| 1078 | been overridden in a class. The search order is same as that used by |
| 1079 | :func:`getattr` except that the *type* itself is skipped. |
| 1080 | |
Raymond Hettinger | 0a68b01 | 2009-02-25 00:58:47 +0000 | [diff] [blame] | 1081 | The :attr:`__mro__` attribute of the *type* lists the method resolution |
| 1082 | search order used by both :func:`getattr` and :func:`super`. The attribute |
| 1083 | is dynamic and can change whenever the inheritance hierarchy is updated. |
Benjamin Peterson | 3e4f055 | 2008-09-02 00:31:15 +0000 | [diff] [blame] | 1084 | |
Raymond Hettinger | 79d0434 | 2009-02-25 00:32:51 +0000 | [diff] [blame] | 1085 | 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] | 1086 | 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] | 1087 | the second argument is a type, ``issubclass(type2, type)`` must be true (this |
| 1088 | is useful for classmethods). |
Georg Brandl | 116aa62 | 2007-08-15 14:28:22 +0000 | [diff] [blame] | 1089 | |
Raymond Hettinger | 0a68b01 | 2009-02-25 00:58:47 +0000 | [diff] [blame] | 1090 | There are two typical use cases for *super*. In a class hierarchy with |
| 1091 | single inheritance, *super* can be used to refer to parent classes without |
Benjamin Peterson | 9bc9351 | 2008-09-22 22:10:59 +0000 | [diff] [blame] | 1092 | naming them explicitly, thus making the code more maintainable. This use |
Raymond Hettinger | 0a68b01 | 2009-02-25 00:58:47 +0000 | [diff] [blame] | 1093 | closely parallels the use of *super* in other programming languages. |
Georg Brandl | 48310cd | 2009-01-03 21:18:54 +0000 | [diff] [blame] | 1094 | |
Raymond Hettinger | 4d9a823 | 2009-02-24 23:30:43 +0000 | [diff] [blame] | 1095 | The second use case is to support cooperative multiple inheritance in a |
Georg Brandl | 48310cd | 2009-01-03 21:18:54 +0000 | [diff] [blame] | 1096 | dynamic execution environment. This use case is unique to Python and is |
| 1097 | not found in statically compiled languages or languages that only support |
Raymond Hettinger | d125845 | 2009-02-26 00:27:18 +0000 | [diff] [blame] | 1098 | single inheritance. This makes it possible to implement "diamond diagrams" |
Benjamin Peterson | 9bc9351 | 2008-09-22 22:10:59 +0000 | [diff] [blame] | 1099 | where multiple base classes implement the same method. Good design dictates |
| 1100 | 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] | 1101 | order of calls is determined at runtime, because that order adapts |
| 1102 | to changes in the class hierarchy, and because that order can include |
| 1103 | sibling classes that are unknown prior to runtime). |
Benjamin Peterson | 9bc9351 | 2008-09-22 22:10:59 +0000 | [diff] [blame] | 1104 | |
| 1105 | For both use cases, a typical superclass call looks like this:: |
Georg Brandl | 116aa62 | 2007-08-15 14:28:22 +0000 | [diff] [blame] | 1106 | |
| 1107 | class C(B): |
Mark Summerfield | 1041f74 | 2008-02-26 13:27:00 +0000 | [diff] [blame] | 1108 | def method(self, arg): |
Georg Brandl | 036490d | 2009-05-17 13:00:36 +0000 | [diff] [blame] | 1109 | super().method(arg) # This does the same thing as: |
| 1110 | # super(C, self).method(arg) |
Georg Brandl | 116aa62 | 2007-08-15 14:28:22 +0000 | [diff] [blame] | 1111 | |
| 1112 | 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] | 1113 | explicit dotted attribute lookups such as ``super().__getitem__(name)``. |
Benjamin Peterson | 9bc9351 | 2008-09-22 22:10:59 +0000 | [diff] [blame] | 1114 | It does so by implementing its own :meth:`__getattribute__` method for searching |
Raymond Hettinger | 4d9a823 | 2009-02-24 23:30:43 +0000 | [diff] [blame] | 1115 | classes in a predictable order that supports cooperative multiple inheritance. |
Georg Brandl | 116aa62 | 2007-08-15 14:28:22 +0000 | [diff] [blame] | 1116 | Accordingly, :func:`super` is undefined for implicit lookups using statements or |
Raymond Hettinger | 518d8da | 2008-12-06 11:44:00 +0000 | [diff] [blame] | 1117 | operators such as ``super()[name]``. |
| 1118 | |
Raymond Hettinger | 79d0434 | 2009-02-25 00:32:51 +0000 | [diff] [blame] | 1119 | Also note that :func:`super` is not limited to use inside methods. The two |
| 1120 | argument form specifies the arguments exactly and makes the appropriate |
Raymond Hettinger | 518d8da | 2008-12-06 11:44:00 +0000 | [diff] [blame] | 1121 | references. The zero argument form automatically searches the stack frame |
| 1122 | for the class (``__class__``) and the first argument. |
Georg Brandl | 116aa62 | 2007-08-15 14:28:22 +0000 | [diff] [blame] | 1123 | |
Georg Brandl | 116aa62 | 2007-08-15 14:28:22 +0000 | [diff] [blame] | 1124 | |
| 1125 | .. function:: tuple([iterable]) |
| 1126 | |
| 1127 | Return a tuple whose items are the same and in the same order as *iterable*'s |
| 1128 | items. *iterable* may be a sequence, a container that supports iteration, or an |
| 1129 | iterator object. If *iterable* is already a tuple, it is returned unchanged. |
| 1130 | For instance, ``tuple('abc')`` returns ``('a', 'b', 'c')`` and ``tuple([1, 2, |
| 1131 | 3])`` returns ``(1, 2, 3)``. If no argument is given, returns a new empty |
| 1132 | tuple, ``()``. |
| 1133 | |
Georg Brandl | 48310cd | 2009-01-03 21:18:54 +0000 | [diff] [blame] | 1134 | :class:`tuple` is an immutable sequence type, as documented in :ref:`typesseq`. |
Georg Brandl | 116aa62 | 2007-08-15 14:28:22 +0000 | [diff] [blame] | 1135 | |
| 1136 | |
| 1137 | .. function:: type(object) |
| 1138 | |
| 1139 | .. index:: object: type |
| 1140 | |
Georg Brandl | 85eb8c1 | 2007-08-31 16:33:38 +0000 | [diff] [blame] | 1141 | Return the type of an *object*. The return value is a type object and |
| 1142 | generally the same object as returned by ``object.__class__``. |
Georg Brandl | 116aa62 | 2007-08-15 14:28:22 +0000 | [diff] [blame] | 1143 | |
Georg Brandl | 85eb8c1 | 2007-08-31 16:33:38 +0000 | [diff] [blame] | 1144 | The :func:`isinstance` built-in function is recommended for testing the type |
| 1145 | of an object, because it takes subclasses into account. |
| 1146 | |
| 1147 | With three arguments, :func:`type` functions as a constructor as detailed |
| 1148 | below. |
Georg Brandl | 116aa62 | 2007-08-15 14:28:22 +0000 | [diff] [blame] | 1149 | |
| 1150 | |
| 1151 | .. function:: type(name, bases, dict) |
| 1152 | :noindex: |
| 1153 | |
| 1154 | Return a new type object. This is essentially a dynamic form of the |
Christian Heimes | fe337bf | 2008-03-23 21:54:12 +0000 | [diff] [blame] | 1155 | :keyword:`class` statement. The *name* string is the class name and becomes the |
| 1156 | :attr:`__name__` attribute; the *bases* tuple itemizes the base classes and |
| 1157 | becomes the :attr:`__bases__` attribute; and the *dict* dictionary is the |
| 1158 | namespace containing definitions for class body and becomes the :attr:`__dict__` |
| 1159 | attribute. For example, the following two statements create identical |
| 1160 | :class:`type` objects: |
Georg Brandl | 116aa62 | 2007-08-15 14:28:22 +0000 | [diff] [blame] | 1161 | |
| 1162 | >>> class X(object): |
| 1163 | ... a = 1 |
Georg Brandl | 48310cd | 2009-01-03 21:18:54 +0000 | [diff] [blame] | 1164 | ... |
Georg Brandl | 116aa62 | 2007-08-15 14:28:22 +0000 | [diff] [blame] | 1165 | >>> X = type('X', (object,), dict(a=1)) |
| 1166 | |
Georg Brandl | 116aa62 | 2007-08-15 14:28:22 +0000 | [diff] [blame] | 1167 | |
| 1168 | .. function:: vars([object]) |
| 1169 | |
| 1170 | Without arguments, return a dictionary corresponding to the current local symbol |
| 1171 | table. With a module, class or class instance object as argument (or anything |
| 1172 | else that has a :attr:`__dict__` attribute), returns a dictionary corresponding |
Benjamin Peterson | d23f822 | 2009-04-05 19:13:16 +0000 | [diff] [blame] | 1173 | to the object's symbol table. |
Georg Brandl | 116aa62 | 2007-08-15 14:28:22 +0000 | [diff] [blame] | 1174 | |
Georg Brandl | e720c0a | 2009-04-27 16:20:50 +0000 | [diff] [blame] | 1175 | .. note:: |
Benjamin Peterson | d23f822 | 2009-04-05 19:13:16 +0000 | [diff] [blame] | 1176 | The returned dictionary should not be modified: |
| 1177 | the effects on the corresponding symbol table are undefined. [#]_ |
Georg Brandl | 116aa62 | 2007-08-15 14:28:22 +0000 | [diff] [blame] | 1178 | |
Raymond Hettinger | dd1150e | 2008-03-13 02:39:40 +0000 | [diff] [blame] | 1179 | .. function:: zip(*iterables) |
Georg Brandl | 116aa62 | 2007-08-15 14:28:22 +0000 | [diff] [blame] | 1180 | |
Georg Brandl | 48310cd | 2009-01-03 21:18:54 +0000 | [diff] [blame] | 1181 | Make an iterator that aggregates elements from each of the iterables. |
Raymond Hettinger | dd1150e | 2008-03-13 02:39:40 +0000 | [diff] [blame] | 1182 | |
| 1183 | Returns an iterator of tuples, where the *i*-th tuple contains |
Georg Brandl | 952aea2 | 2007-09-04 17:50:40 +0000 | [diff] [blame] | 1184 | 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] | 1185 | iterator stops when the shortest input iterable is exhausted. With a single |
Georg Brandl | 48310cd | 2009-01-03 21:18:54 +0000 | [diff] [blame] | 1186 | iterable argument, it returns an iterator of 1-tuples. With no arguments, |
Raymond Hettinger | dd1150e | 2008-03-13 02:39:40 +0000 | [diff] [blame] | 1187 | it returns an empty iterator. Equivalent to:: |
| 1188 | |
| 1189 | def zip(*iterables): |
| 1190 | # zip('ABCD', 'xy') --> Ax By |
| 1191 | iterables = map(iter, iterables) |
| 1192 | while iterables: |
Raymond Hettinger | cdf8ba3 | 2009-02-19 04:45:07 +0000 | [diff] [blame] | 1193 | yield tuple(map(next, iterables)) |
Georg Brandl | 116aa62 | 2007-08-15 14:28:22 +0000 | [diff] [blame] | 1194 | |
Christian Heimes | 1af737c | 2008-01-23 08:24:23 +0000 | [diff] [blame] | 1195 | The left-to-right evaluation order of the iterables is guaranteed. This |
| 1196 | makes possible an idiom for clustering a data series into n-length groups |
| 1197 | using ``zip(*[iter(s)]*n)``. |
| 1198 | |
Raymond Hettinger | dd1150e | 2008-03-13 02:39:40 +0000 | [diff] [blame] | 1199 | :func:`zip` should only be used with unequal length inputs when you don't |
| 1200 | care about trailing, unmatched values from the longer iterables. If those |
| 1201 | values are important, use :func:`itertools.zip_longest` instead. |
Georg Brandl | 116aa62 | 2007-08-15 14:28:22 +0000 | [diff] [blame] | 1202 | |
Benjamin Peterson | f10a79a | 2008-10-11 00:49:57 +0000 | [diff] [blame] | 1203 | :func:`zip` in conjunction with the ``*`` operator can be used to unzip a |
| 1204 | list:: |
| 1205 | |
| 1206 | >>> x = [1, 2, 3] |
| 1207 | >>> y = [4, 5, 6] |
| 1208 | >>> zipped = zip(x, y) |
Georg Brandl | 17fe364 | 2008-12-06 14:28:56 +0000 | [diff] [blame] | 1209 | >>> list(zipped) |
Benjamin Peterson | f10a79a | 2008-10-11 00:49:57 +0000 | [diff] [blame] | 1210 | [(1, 4), (2, 5), (3, 6)] |
Georg Brandl | 17fe364 | 2008-12-06 14:28:56 +0000 | [diff] [blame] | 1211 | >>> x2, y2 = zip(*zip(x, y)) |
Benjamin Peterson | fa0d703 | 2009-06-01 22:42:33 +0000 | [diff] [blame] | 1212 | >>> x == list(x2) and y == list(y2) |
Benjamin Peterson | f10a79a | 2008-10-11 00:49:57 +0000 | [diff] [blame] | 1213 | True |
| 1214 | |
Georg Brandl | 2ee470f | 2008-07-16 12:55:28 +0000 | [diff] [blame] | 1215 | |
Georg Brandl | 036490d | 2009-05-17 13:00:36 +0000 | [diff] [blame] | 1216 | .. function:: __import__(name, globals={}, locals={}, fromlist=[], level=-1) |
Georg Brandl | 4836781 | 2008-12-05 15:55:41 +0000 | [diff] [blame] | 1217 | |
| 1218 | .. index:: |
| 1219 | statement: import |
| 1220 | module: imp |
| 1221 | |
| 1222 | .. note:: |
| 1223 | |
| 1224 | This is an advanced function that is not needed in everyday Python |
| 1225 | programming. |
| 1226 | |
Benjamin Peterson | 6ebe78f | 2008-12-21 00:06:59 +0000 | [diff] [blame] | 1227 | This function is invoked by the :keyword:`import` statement. It can be |
| 1228 | replaced (by importing the :mod:`builtins` module and assigning to |
| 1229 | ``builtins.__import__``) in order to change semantics of the |
| 1230 | :keyword:`import` statement, but nowadays it is usually simpler to use import |
| 1231 | hooks (see :pep:`302`). Direct use of :func:`__import__` is rare, except in |
| 1232 | cases where you want to import a module whose name is only known at runtime. |
Georg Brandl | 4836781 | 2008-12-05 15:55:41 +0000 | [diff] [blame] | 1233 | |
Benjamin Peterson | 6ebe78f | 2008-12-21 00:06:59 +0000 | [diff] [blame] | 1234 | The function imports the module *name*, potentially using the given *globals* |
| 1235 | and *locals* to determine how to interpret the name in a package context. |
| 1236 | The *fromlist* gives the names of objects or submodules that should be |
| 1237 | imported from the module given by *name*. The standard implementation does |
| 1238 | not use its *locals* argument at all, and uses its *globals* only to |
| 1239 | determine the package context of the :keyword:`import` statement. |
| 1240 | |
Brett Cannon | 2b9fd47 | 2009-03-15 02:18:41 +0000 | [diff] [blame] | 1241 | *level* specifies whether to use absolute or relative imports. ``0`` (the |
| 1242 | default) means only perform absolute imports. Positive values for |
Benjamin Peterson | 6ebe78f | 2008-12-21 00:06:59 +0000 | [diff] [blame] | 1243 | *level* indicate the number of parent directories to search relative to the |
| 1244 | directory of the module calling :func:`__import__`. |
Georg Brandl | 4836781 | 2008-12-05 15:55:41 +0000 | [diff] [blame] | 1245 | |
| 1246 | When the *name* variable is of the form ``package.module``, normally, the |
| 1247 | top-level package (the name up till the first dot) is returned, *not* the |
| 1248 | module named by *name*. However, when a non-empty *fromlist* argument is |
Benjamin Peterson | 6ebe78f | 2008-12-21 00:06:59 +0000 | [diff] [blame] | 1249 | given, the module named by *name* is returned. |
Georg Brandl | 4836781 | 2008-12-05 15:55:41 +0000 | [diff] [blame] | 1250 | |
Benjamin Peterson | 6ebe78f | 2008-12-21 00:06:59 +0000 | [diff] [blame] | 1251 | For example, the statement ``import spam`` results in bytecode resembling the |
| 1252 | following code:: |
Georg Brandl | 48310cd | 2009-01-03 21:18:54 +0000 | [diff] [blame] | 1253 | |
Brett Cannon | 2b9fd47 | 2009-03-15 02:18:41 +0000 | [diff] [blame] | 1254 | spam = __import__('spam', globals(), locals(), [], 0) |
Georg Brandl | 4836781 | 2008-12-05 15:55:41 +0000 | [diff] [blame] | 1255 | |
Benjamin Peterson | 6ebe78f | 2008-12-21 00:06:59 +0000 | [diff] [blame] | 1256 | The statement ``import spam.ham`` results in this call:: |
Georg Brandl | 4836781 | 2008-12-05 15:55:41 +0000 | [diff] [blame] | 1257 | |
Brett Cannon | 2b9fd47 | 2009-03-15 02:18:41 +0000 | [diff] [blame] | 1258 | spam = __import__('spam.ham', globals(), locals(), [], 0) |
Benjamin Peterson | 6ebe78f | 2008-12-21 00:06:59 +0000 | [diff] [blame] | 1259 | |
| 1260 | Note how :func:`__import__` returns the toplevel module here because this is |
| 1261 | the object that is bound to a name by the :keyword:`import` statement. |
| 1262 | |
| 1263 | On the other hand, the statement ``from spam.ham import eggs, sausage as |
| 1264 | saus`` results in :: |
| 1265 | |
Brett Cannon | 2b9fd47 | 2009-03-15 02:18:41 +0000 | [diff] [blame] | 1266 | _temp = __import__('spam.ham', globals(), locals(), ['eggs', 'sausage'], 0) |
Benjamin Peterson | 6ebe78f | 2008-12-21 00:06:59 +0000 | [diff] [blame] | 1267 | eggs = _temp.eggs |
| 1268 | saus = _temp.sausage |
| 1269 | |
| 1270 | Here, the ``spam.ham`` module is returned from :func:`__import__`. From this |
| 1271 | object, the names to import are retrieved and assigned to their respective |
| 1272 | names. |
| 1273 | |
| 1274 | If you simply want to import a module (potentially within a package) by name, |
Benjamin Peterson | fa0d703 | 2009-06-01 22:42:33 +0000 | [diff] [blame] | 1275 | you can call :func:`__import__` and then look it up in :data:`sys.modules`:: |
Benjamin Peterson | 6ebe78f | 2008-12-21 00:06:59 +0000 | [diff] [blame] | 1276 | |
| 1277 | >>> import sys |
| 1278 | >>> name = 'foo.bar.baz' |
| 1279 | >>> __import__(name) |
| 1280 | <module 'foo' from ...> |
| 1281 | >>> baz = sys.modules[name] |
| 1282 | >>> baz |
| 1283 | <module 'foo.bar.baz' from ...> |
Georg Brandl | 4836781 | 2008-12-05 15:55:41 +0000 | [diff] [blame] | 1284 | |
Georg Brandl | 116aa62 | 2007-08-15 14:28:22 +0000 | [diff] [blame] | 1285 | .. rubric:: Footnotes |
| 1286 | |
Georg Brandl | 47f27a3 | 2009-03-31 16:57:13 +0000 | [diff] [blame] | 1287 | .. [#] Note that the parser only accepts the Unix-style end of line convention. |
| 1288 | If you are reading the code from a file, make sure to use newline conversion |
| 1289 | mode to convert Windows or Mac-style newlines. |
Georg Brandl | 116aa62 | 2007-08-15 14:28:22 +0000 | [diff] [blame] | 1290 | |
| 1291 | .. [#] In the current implementation, local variable bindings cannot normally be |
| 1292 | affected this way, but variables retrieved from other scopes (such as modules) |
| 1293 | can be. This may change. |