Georg Brandl | 116aa62 | 2007-08-15 14:28:22 +0000 | [diff] [blame] | 1 | |
| 2 | .. _built-in-funcs: |
| 3 | |
| 4 | Built-in Functions |
| 5 | ================== |
| 6 | |
| 7 | The Python interpreter has a number of functions built into it that are always |
| 8 | available. They are listed here in alphabetical order. |
| 9 | |
| 10 | |
| 11 | .. function:: __import__(name[, globals[, locals[, fromlist[, level]]]]) |
| 12 | |
| 13 | .. index:: |
| 14 | statement: import |
Georg Brandl | 116aa62 | 2007-08-15 14:28:22 +0000 | [diff] [blame] | 15 | module: imp |
| 16 | |
| 17 | .. note:: |
| 18 | |
| 19 | This is an advanced function that is not needed in everyday Python |
| 20 | programming. |
| 21 | |
| 22 | The function is invoked by the :keyword:`import` statement. It mainly exists |
| 23 | so that you can replace it with another function that has a compatible |
Georg Brandl | 55ac8f0 | 2007-09-01 13:51:09 +0000 | [diff] [blame] | 24 | interface, in order to change the semantics of the :keyword:`import` |
| 25 | statement. For examples of why and how you would do this, see the standard |
| 26 | library module :mod:`ihooks`. See also the built-in module :mod:`imp`, which |
Georg Brandl | 116aa62 | 2007-08-15 14:28:22 +0000 | [diff] [blame] | 27 | defines some useful operations out of which you can build your own |
| 28 | :func:`__import__` function. |
| 29 | |
| 30 | For example, the statement ``import spam`` results in the following call: |
| 31 | ``__import__('spam',`` ``globals(),`` ``locals(), [], -1)``; the statement |
| 32 | ``from spam.ham import eggs`` results in ``__import__('spam.ham', globals(), |
| 33 | locals(), ['eggs'], -1)``. Note that even though ``locals()`` and ``['eggs']`` |
| 34 | are passed in as arguments, the :func:`__import__` function does not set the |
| 35 | local variable named ``eggs``; this is done by subsequent code that is generated |
| 36 | for the import statement. (In fact, the standard implementation does not use |
| 37 | its *locals* argument at all, and uses its *globals* only to determine the |
| 38 | package context of the :keyword:`import` statement.) |
| 39 | |
| 40 | When the *name* variable is of the form ``package.module``, normally, the |
| 41 | top-level package (the name up till the first dot) is returned, *not* the |
| 42 | module named by *name*. However, when a non-empty *fromlist* argument is |
| 43 | given, the module named by *name* is returned. This is done for |
Georg Brandl | 9afde1c | 2007-11-01 20:32:30 +0000 | [diff] [blame] | 44 | compatibility with the :term:`bytecode` generated for the different kinds of import |
Georg Brandl | 116aa62 | 2007-08-15 14:28:22 +0000 | [diff] [blame] | 45 | statement; when using ``import spam.ham.eggs``, the top-level package |
| 46 | :mod:`spam` must be placed in the importing namespace, but when using ``from |
| 47 | spam.ham import eggs``, the ``spam.ham`` subpackage must be used to find the |
| 48 | ``eggs`` variable. As a workaround for this behavior, use :func:`getattr` to |
| 49 | extract the desired components. For example, you could define the following |
| 50 | helper:: |
| 51 | |
| 52 | def my_import(name): |
| 53 | mod = __import__(name) |
| 54 | components = name.split('.') |
| 55 | for comp in components[1:]: |
| 56 | mod = getattr(mod, comp) |
| 57 | return mod |
| 58 | |
| 59 | *level* specifies whether to use absolute or relative imports. The default is |
| 60 | ``-1`` which indicates both absolute and relative imports will be attempted. |
| 61 | ``0`` means only perform absolute imports. Positive values for *level* indicate |
| 62 | the number of parent directories to search relative to the directory of the |
| 63 | module calling :func:`__import__`. |
| 64 | |
Georg Brandl | 116aa62 | 2007-08-15 14:28:22 +0000 | [diff] [blame] | 65 | |
| 66 | .. function:: abs(x) |
| 67 | |
Georg Brandl | ba956ae | 2007-11-29 17:24:34 +0000 | [diff] [blame] | 68 | Return the absolute value of a number. The argument may be an |
Georg Brandl | 116aa62 | 2007-08-15 14:28:22 +0000 | [diff] [blame] | 69 | integer or a floating point number. If the argument is a complex number, its |
| 70 | magnitude is returned. |
| 71 | |
| 72 | |
| 73 | .. function:: all(iterable) |
| 74 | |
| 75 | Return True if all elements of the *iterable* are true. Equivalent to:: |
| 76 | |
| 77 | def all(iterable): |
| 78 | for element in iterable: |
| 79 | if not element: |
| 80 | return False |
| 81 | return True |
| 82 | |
Georg Brandl | 116aa62 | 2007-08-15 14:28:22 +0000 | [diff] [blame] | 83 | |
| 84 | .. function:: any(iterable) |
| 85 | |
| 86 | Return True if any element of the *iterable* is true. Equivalent to:: |
| 87 | |
| 88 | def any(iterable): |
| 89 | for element in iterable: |
| 90 | if element: |
| 91 | return True |
| 92 | return False |
| 93 | |
Georg Brandl | 116aa62 | 2007-08-15 14:28:22 +0000 | [diff] [blame] | 94 | |
| 95 | .. function:: basestring() |
| 96 | |
| 97 | This abstract type is the superclass for :class:`str`. It |
| 98 | cannot be called or instantiated, but it can be used to test whether an object |
| 99 | is an instance of :class:`str` (or a user-defined type inherited from |
| 100 | :class:`basestring`). |
| 101 | |
Georg Brandl | 116aa62 | 2007-08-15 14:28:22 +0000 | [diff] [blame] | 102 | |
| 103 | .. function:: bin(x) |
| 104 | |
| 105 | Convert an integer number to a binary string. The result is a valid Python |
| 106 | expression. If *x* is not a Python :class:`int` object, it has to define an |
| 107 | :meth:`__index__` method that returns an integer. |
| 108 | |
Georg Brandl | 116aa62 | 2007-08-15 14:28:22 +0000 | [diff] [blame] | 109 | |
| 110 | .. function:: bool([x]) |
| 111 | |
| 112 | Convert a value to a Boolean, using the standard truth testing procedure. If |
| 113 | *x* is false or omitted, this returns :const:`False`; otherwise it returns |
| 114 | :const:`True`. :class:`bool` is also a class, which is a subclass of |
| 115 | :class:`int`. Class :class:`bool` cannot be subclassed further. Its only |
| 116 | instances are :const:`False` and :const:`True`. |
| 117 | |
| 118 | .. index:: pair: Boolean; type |
| 119 | |
Georg Brandl | 116aa62 | 2007-08-15 14:28:22 +0000 | [diff] [blame] | 120 | |
Georg Brandl | 9541463 | 2007-11-22 11:00:28 +0000 | [diff] [blame] | 121 | .. function:: bytearray([arg[, encoding[, errors]]]) |
Georg Brandl | 85eb8c1 | 2007-08-31 16:33:38 +0000 | [diff] [blame] | 122 | |
Georg Brandl | 24eac03 | 2007-11-22 14:16:00 +0000 | [diff] [blame] | 123 | 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] | 124 | sequence of integers in the range 0 <= x < 256. It has most of the usual |
| 125 | methods of mutable sequences, described in :ref:`typesseq-mutable`, as well |
| 126 | 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] | 127 | |
| 128 | The optional *arg* parameter can be used to initialize the array in a few |
| 129 | different ways: |
| 130 | |
| 131 | * If it is a *string*, you must also give the *encoding* (and optionally, |
Georg Brandl | 9541463 | 2007-11-22 11:00:28 +0000 | [diff] [blame] | 132 | *errors*) parameters; :func:`bytearray` then converts the Unicode string to |
Guido van Rossum | 98297ee | 2007-11-06 21:34:58 +0000 | [diff] [blame] | 133 | bytes using :meth:`str.encode`. |
Georg Brandl | 85eb8c1 | 2007-08-31 16:33:38 +0000 | [diff] [blame] | 134 | |
| 135 | * If it is an *integer*, the array will have that size and will be |
| 136 | initialized with null bytes. |
| 137 | |
| 138 | * If it is an object conforming to the *buffer* interface, a read-only buffer |
| 139 | of the object will be used to initialize the bytes array. |
| 140 | |
Guido van Rossum | 98297ee | 2007-11-06 21:34:58 +0000 | [diff] [blame] | 141 | * If it is an *iterable*, it must be an iterable of integers in the range |
| 142 | ``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] | 143 | |
| 144 | Without an argument, an array of size 0 is created. |
| 145 | |
| 146 | |
Guido van Rossum | 98297ee | 2007-11-06 21:34:58 +0000 | [diff] [blame] | 147 | .. function:: bytes([arg[, encoding[, errors]]]) |
| 148 | |
| 149 | Return a new "bytes" object, which is an immutable sequence of integers in |
| 150 | the range ``0 <= x < 256``. :class:`bytes` is an immutable version of |
Georg Brandl | 9541463 | 2007-11-22 11:00:28 +0000 | [diff] [blame] | 151 | :class:`bytearray` -- it has the same non-mutating methods and the same |
| 152 | indexing and slicing behavior. |
Guido van Rossum | 98297ee | 2007-11-06 21:34:58 +0000 | [diff] [blame] | 153 | |
| 154 | Accordingly, constructor arguments are interpreted as for :func:`buffer`. |
| 155 | |
| 156 | Bytes objects can also be created with literals, see :ref:`strings`. |
| 157 | |
| 158 | |
Georg Brandl | 116aa62 | 2007-08-15 14:28:22 +0000 | [diff] [blame] | 159 | .. function:: chr(i) |
| 160 | |
Georg Brandl | 85eb8c1 | 2007-08-31 16:33:38 +0000 | [diff] [blame] | 161 | Return the string of one character whose Unicode codepoint is the integer |
| 162 | *i*. For example, ``chr(97)`` returns the string ``'a'``. This is the |
| 163 | inverse of :func:`ord`. The valid range for the argument depends how Python |
| 164 | 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] | 165 | :exc:`ValueError` will be raised if *i* is outside that range. |
| 166 | |
| 167 | |
| 168 | .. function:: classmethod(function) |
| 169 | |
| 170 | Return a class method for *function*. |
| 171 | |
| 172 | A class method receives the class as implicit first argument, just like an |
| 173 | instance method receives the instance. To declare a class method, use this |
| 174 | idiom:: |
| 175 | |
| 176 | class C: |
| 177 | @classmethod |
| 178 | def f(cls, arg1, arg2, ...): ... |
| 179 | |
| 180 | The ``@classmethod`` form is a function decorator -- see the description of |
| 181 | function definitions in :ref:`function` for details. |
| 182 | |
| 183 | It can be called either on the class (such as ``C.f()``) or on an instance (such |
| 184 | as ``C().f()``). The instance is ignored except for its class. If a class |
| 185 | method is called for a derived class, the derived class object is passed as the |
| 186 | implied first argument. |
| 187 | |
| 188 | Class methods are different than C++ or Java static methods. If you want those, |
| 189 | see :func:`staticmethod` in this section. |
| 190 | |
| 191 | For more information on class methods, consult the documentation on the standard |
| 192 | type hierarchy in :ref:`types`. |
| 193 | |
Georg Brandl | 116aa62 | 2007-08-15 14:28:22 +0000 | [diff] [blame] | 194 | |
| 195 | .. function:: cmp(x, y) |
| 196 | |
| 197 | Compare the two objects *x* and *y* and return an integer according to the |
| 198 | outcome. The return value is negative if ``x < y``, zero if ``x == y`` and |
| 199 | strictly positive if ``x > y``. |
| 200 | |
| 201 | |
| 202 | .. function:: compile(source, filename, mode[, flags[, dont_inherit]]) |
| 203 | |
| 204 | Compile the *source* into a code object. Code objects can be executed by a call |
| 205 | to :func:`exec` or evaluated by a call to :func:`eval`. The *filename* argument |
| 206 | should give the file from which the code was read; pass some recognizable value |
| 207 | if it wasn't read from a file (``'<string>'`` is commonly used). The *mode* |
| 208 | argument specifies what kind of code must be compiled; it can be ``'exec'`` if |
| 209 | *source* consists of a sequence of statements, ``'eval'`` if it consists of a |
| 210 | single expression, or ``'single'`` if it consists of a single interactive |
| 211 | statement (in the latter case, expression statements that evaluate to something |
| 212 | else than ``None`` will be printed). |
| 213 | |
| 214 | When compiling multi-line statements, two caveats apply: line endings must be |
| 215 | represented by a single newline character (``'\n'``), and the input must be |
| 216 | terminated by at least one newline character. If line endings are represented |
| 217 | by ``'\r\n'``, use the string :meth:`replace` method to change them into |
| 218 | ``'\n'``. |
| 219 | |
| 220 | The optional arguments *flags* and *dont_inherit* (which are new in Python 2.2) |
| 221 | control which future statements (see :pep:`236`) affect the compilation of |
| 222 | *source*. If neither is present (or both are zero) the code is compiled with |
| 223 | those future statements that are in effect in the code that is calling compile. |
| 224 | If the *flags* argument is given and *dont_inherit* is not (or is zero) then the |
| 225 | future statements specified by the *flags* argument are used in addition to |
| 226 | those that would be used anyway. If *dont_inherit* is a non-zero integer then |
| 227 | the *flags* argument is it -- the future statements in effect around the call to |
| 228 | compile are ignored. |
| 229 | |
| 230 | Future statements are specified by bits which can be bitwise or-ed together to |
| 231 | specify multiple statements. The bitfield required to specify a given feature |
| 232 | can be found as the :attr:`compiler_flag` attribute on the :class:`_Feature` |
| 233 | instance in the :mod:`__future__` module. |
| 234 | |
| 235 | |
| 236 | .. function:: complex([real[, imag]]) |
| 237 | |
| 238 | Create a complex number with the value *real* + *imag*\*j or convert a string or |
| 239 | number to a complex number. If the first parameter is a string, it will be |
| 240 | interpreted as a complex number and the function must be called without a second |
| 241 | parameter. The second parameter can never be a string. Each argument may be any |
| 242 | 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^] | 243 | the function serves as a numeric conversion function like :func:`int` |
| 244 | and :func:`float`. If both arguments are omitted, returns ``0j``. |
Georg Brandl | 116aa62 | 2007-08-15 14:28:22 +0000 | [diff] [blame] | 245 | |
| 246 | The complex type is described in :ref:`typesnumeric`. |
| 247 | |
| 248 | |
| 249 | .. function:: delattr(object, name) |
| 250 | |
| 251 | This is a relative of :func:`setattr`. The arguments are an object and a |
| 252 | string. The string must be the name of one of the object's attributes. The |
| 253 | function deletes the named attribute, provided the object allows it. For |
| 254 | example, ``delattr(x, 'foobar')`` is equivalent to ``del x.foobar``. |
| 255 | |
| 256 | |
| 257 | .. function:: dict([arg]) |
| 258 | :noindex: |
| 259 | |
| 260 | Create a new data dictionary, optionally with items taken from *arg*. |
| 261 | The dictionary type is described in :ref:`typesmapping`. |
| 262 | |
| 263 | For other containers see the built in :class:`list`, :class:`set`, and |
| 264 | :class:`tuple` classes, and the :mod:`collections` module. |
| 265 | |
| 266 | |
| 267 | .. function:: dir([object]) |
| 268 | |
| 269 | Without arguments, return the list of names in the current local scope. With an |
| 270 | argument, attempt to return a list of valid attributes for that object. |
| 271 | |
| 272 | If the object has a method named :meth:`__dir__`, this method will be called and |
| 273 | must return the list of attributes. This allows objects that implement a custom |
| 274 | :func:`__getattr__` or :func:`__getattribute__` function to customize the way |
| 275 | :func:`dir` reports their attributes. |
| 276 | |
| 277 | If the object does not provide :meth:`__dir__`, the function tries its best to |
| 278 | gather information from the object's :attr:`__dict__` attribute, if defined, and |
| 279 | from its type object. The resulting list is not necessarily complete, and may |
| 280 | be inaccurate when the object has a custom :func:`__getattr__`. |
| 281 | |
| 282 | The default :func:`dir` mechanism behaves differently with different types of |
| 283 | objects, as it attempts to produce the most relevant, rather than complete, |
| 284 | information: |
| 285 | |
| 286 | * If the object is a module object, the list contains the names of the module's |
| 287 | attributes. |
| 288 | |
| 289 | * If the object is a type or class object, the list contains the names of its |
| 290 | attributes, and recursively of the attributes of its bases. |
| 291 | |
| 292 | * Otherwise, the list contains the object's attributes' names, the names of its |
| 293 | class's attributes, and recursively of the attributes of its class's base |
| 294 | classes. |
| 295 | |
| 296 | The resulting list is sorted alphabetically. For example:: |
| 297 | |
| 298 | >>> import struct |
| 299 | >>> dir() |
| 300 | ['__builtins__', '__doc__', '__name__', 'struct'] |
| 301 | >>> dir(struct) |
| 302 | ['__doc__', '__name__', 'calcsize', 'error', 'pack', 'unpack'] |
| 303 | >>> class Foo(object): |
| 304 | ... def __dir__(self): |
| 305 | ... return ["kan", "ga", "roo"] |
| 306 | ... |
| 307 | >>> f = Foo() |
| 308 | >>> dir(f) |
| 309 | ['ga', 'kan', 'roo'] |
| 310 | |
| 311 | .. note:: |
| 312 | |
| 313 | Because :func:`dir` is supplied primarily as a convenience for use at an |
| 314 | interactive prompt, it tries to supply an interesting set of names more than it |
| 315 | tries to supply a rigorously or consistently defined set of names, and its |
| 316 | detailed behavior may change across releases. |
| 317 | |
| 318 | |
| 319 | .. function:: divmod(a, b) |
| 320 | |
| 321 | Take two (non complex) numbers as arguments and return a pair of numbers |
Georg Brandl | 5c10664 | 2007-11-29 17:41:05 +0000 | [diff] [blame^] | 322 | consisting of their quotient and remainder when using integer division. With mixed |
Georg Brandl | ba956ae | 2007-11-29 17:24:34 +0000 | [diff] [blame] | 323 | operand types, the rules for binary arithmetic operators apply. For integers, |
| 324 | the result is the same as ``(a // b, a % b)``. For floating point |
Georg Brandl | 116aa62 | 2007-08-15 14:28:22 +0000 | [diff] [blame] | 325 | numbers the result is ``(q, a % b)``, where *q* is usually ``math.floor(a / b)`` |
| 326 | but may be 1 less than that. In any case ``q * b + a % b`` is very close to |
| 327 | *a*, if ``a % b`` is non-zero it has the same sign as *b*, and ``0 <= abs(a % b) |
| 328 | < abs(b)``. |
| 329 | |
Georg Brandl | 116aa62 | 2007-08-15 14:28:22 +0000 | [diff] [blame] | 330 | |
| 331 | .. function:: enumerate(iterable) |
| 332 | |
Georg Brandl | 9afde1c | 2007-11-01 20:32:30 +0000 | [diff] [blame] | 333 | Return an enumerate object. *iterable* must be a sequence, an :term:`iterator`, or some |
Georg Brandl | 116aa62 | 2007-08-15 14:28:22 +0000 | [diff] [blame] | 334 | other object which supports iteration. The :meth:`__next__` method of the |
| 335 | iterator returned by :func:`enumerate` returns a tuple containing a count (from |
| 336 | zero) and the corresponding value obtained from iterating over *iterable*. |
| 337 | :func:`enumerate` is useful for obtaining an indexed series: ``(0, seq[0])``, |
| 338 | ``(1, seq[1])``, ``(2, seq[2])``, .... For example:: |
| 339 | |
| 340 | >>> for i, season in enumerate(['Spring', 'Summer', 'Fall', 'Winter')]: |
Georg Brandl | 6911e3c | 2007-09-04 07:15:32 +0000 | [diff] [blame] | 341 | >>> print(i, season) |
Georg Brandl | 116aa62 | 2007-08-15 14:28:22 +0000 | [diff] [blame] | 342 | 0 Spring |
| 343 | 1 Summer |
| 344 | 2 Fall |
| 345 | 3 Winter |
| 346 | |
Georg Brandl | 116aa62 | 2007-08-15 14:28:22 +0000 | [diff] [blame] | 347 | |
| 348 | .. function:: eval(expression[, globals[, locals]]) |
| 349 | |
| 350 | The arguments are a string and optional globals and locals. If provided, |
| 351 | *globals* must be a dictionary. If provided, *locals* can be any mapping |
| 352 | object. |
| 353 | |
Georg Brandl | 116aa62 | 2007-08-15 14:28:22 +0000 | [diff] [blame] | 354 | The *expression* argument is parsed and evaluated as a Python expression |
| 355 | (technically speaking, a condition list) using the *globals* and *locals* |
Georg Brandl | 9afde1c | 2007-11-01 20:32:30 +0000 | [diff] [blame] | 356 | dictionaries as global and local namespace. If the *globals* dictionary is |
Georg Brandl | 116aa62 | 2007-08-15 14:28:22 +0000 | [diff] [blame] | 357 | present and lacks '__builtins__', the current globals are copied into *globals* |
| 358 | before *expression* is parsed. This means that *expression* normally has full |
| 359 | access to the standard :mod:`__builtin__` module and restricted environments are |
| 360 | propagated. If the *locals* dictionary is omitted it defaults to the *globals* |
| 361 | dictionary. If both dictionaries are omitted, the expression is executed in the |
| 362 | environment where :keyword:`eval` is called. The return value is the result of |
| 363 | the evaluated expression. Syntax errors are reported as exceptions. Example:: |
| 364 | |
| 365 | >>> x = 1 |
Georg Brandl | 6911e3c | 2007-09-04 07:15:32 +0000 | [diff] [blame] | 366 | >>> eval('x+1') |
Georg Brandl | 116aa62 | 2007-08-15 14:28:22 +0000 | [diff] [blame] | 367 | 2 |
| 368 | |
| 369 | This function can also be used to execute arbitrary code objects (such as those |
| 370 | created by :func:`compile`). In this case pass a code object instead of a |
| 371 | string. The code object must have been compiled passing ``'eval'`` as the |
| 372 | *kind* argument. |
| 373 | |
| 374 | Hints: dynamic execution of statements is supported by the :func:`exec` |
| 375 | function. The :func:`globals` and :func:`locals` functions |
| 376 | returns the current global and local dictionary, respectively, which may be |
| 377 | useful to pass around for use by :func:`eval` or :func:`exec`. |
| 378 | |
| 379 | |
| 380 | .. function:: exec(object[, globals[, locals]]) |
| 381 | |
| 382 | This function supports dynamic execution of Python code. *object* must be either |
| 383 | a string, an open file object, or a code object. If it is a string, the string |
| 384 | is parsed as a suite of Python statements which is then executed (unless a |
| 385 | syntax error occurs). If it is an open file, the file is parsed until EOF and |
| 386 | executed. If it is a code object, it is simply executed. In all cases, the |
| 387 | code that's executed is expected to be valid as file input (see the section |
| 388 | "File input" in the Reference Manual). Be aware that the :keyword:`return` and |
| 389 | :keyword:`yield` statements may not be used outside of function definitions even |
| 390 | within the context of code passed to the :func:`exec` function. The return value |
| 391 | is ``None``. |
| 392 | |
| 393 | In all cases, if the optional parts are omitted, the code is executed in the |
| 394 | current scope. If only *globals* is provided, it must be a dictionary, which |
| 395 | will be used for both the global and the local variables. If *globals* and |
| 396 | *locals* are given, they are used for the global and local variables, |
| 397 | respectively. If provided, *locals* can be any mapping object. |
| 398 | |
| 399 | If the *globals* dictionary does not contain a value for the key |
| 400 | ``__builtins__``, a reference to the dictionary of the built-in module |
| 401 | :mod:`__builtin__` is inserted under that key. That way you can control what |
| 402 | builtins are available to the executed code by inserting your own |
| 403 | ``__builtins__`` dictionary into *globals* before passing it to :func:`exec`. |
| 404 | |
| 405 | .. note:: |
| 406 | |
| 407 | The built-in functions :func:`globals` and :func:`locals` return the current |
| 408 | global and local dictionary, respectively, which may be useful to pass around |
| 409 | for use as the second and third argument to :func:`exec`. |
| 410 | |
| 411 | .. warning:: |
| 412 | |
| 413 | The default *locals* act as described for function :func:`locals` below: |
| 414 | modifications to the default *locals* dictionary should not be attempted. Pass |
| 415 | an explicit *locals* dictionary if you need to see effects of the code on |
| 416 | *locals* after function :func:`execfile` returns. :func:`exec` cannot be |
| 417 | used reliably to modify a function's locals. |
| 418 | |
| 419 | |
| 420 | .. function:: filter(function, iterable) |
| 421 | |
Georg Brandl | 952aea2 | 2007-09-04 17:50:40 +0000 | [diff] [blame] | 422 | Construct an iterator from those elements of *iterable* for which *function* |
| 423 | returns true. *iterable* may be either a sequence, a container which |
Georg Brandl | 9afde1c | 2007-11-01 20:32:30 +0000 | [diff] [blame] | 424 | supports iteration, or an iterator. If *function* is ``None``, the identity |
| 425 | function is assumed, that is, all elements of *iterable* that are false are |
| 426 | removed. |
Georg Brandl | 116aa62 | 2007-08-15 14:28:22 +0000 | [diff] [blame] | 427 | |
Georg Brandl | 952aea2 | 2007-09-04 17:50:40 +0000 | [diff] [blame] | 428 | Note that ``filter(function, iterable)`` is equivalent to the generator |
| 429 | expression ``(item for item in iterable if function(item))`` if function is |
| 430 | not ``None`` and ``(item for item in iterable if item)`` if function is |
| 431 | ``None``. |
Georg Brandl | 116aa62 | 2007-08-15 14:28:22 +0000 | [diff] [blame] | 432 | |
| 433 | |
| 434 | .. function:: float([x]) |
| 435 | |
| 436 | Convert a string or a number to floating point. If the argument is a string, it |
| 437 | must contain a possibly signed decimal or floating point number, possibly |
Georg Brandl | ba956ae | 2007-11-29 17:24:34 +0000 | [diff] [blame] | 438 | embedded in whitespace. Otherwise, the argument may be an integer |
Georg Brandl | 116aa62 | 2007-08-15 14:28:22 +0000 | [diff] [blame] | 439 | or a floating point number, and a floating point number with the same value |
| 440 | (within Python's floating point precision) is returned. If no argument is |
| 441 | given, returns ``0.0``. |
| 442 | |
| 443 | .. note:: |
| 444 | |
| 445 | .. index:: |
| 446 | single: NaN |
| 447 | single: Infinity |
| 448 | |
| 449 | When passing in a string, values for NaN and Infinity may be returned, depending |
| 450 | on the underlying C library. The specific set of strings accepted which cause |
| 451 | these values to be returned depends entirely on the C library and is known to |
| 452 | vary. |
| 453 | |
| 454 | The float type is described in :ref:`typesnumeric`. |
| 455 | |
Georg Brandl | 4b49131 | 2007-08-31 09:22:56 +0000 | [diff] [blame] | 456 | .. function:: format(value[, format_spec]) |
| 457 | |
| 458 | .. index:: |
| 459 | pair: str; format |
| 460 | single: __format__ |
| 461 | |
| 462 | Convert a string or a number to a "formatted" representation, as controlled |
| 463 | by *format_spec*. The interpretation of *format_spec* will depend on the |
| 464 | type of the *value* argument, however there is a standard formatting syntax |
| 465 | that is used by most built-in types: :ref:`formatspec`. |
| 466 | |
| 467 | .. note:: |
| 468 | |
| 469 | ``format(value, format_spec)`` merely calls ``value.__format__(format_spec)``. |
| 470 | |
| 471 | |
Georg Brandl | 116aa62 | 2007-08-15 14:28:22 +0000 | [diff] [blame] | 472 | .. function:: frozenset([iterable]) |
| 473 | :noindex: |
| 474 | |
| 475 | Return a frozenset object, optionally with elements taken from *iterable*. |
| 476 | The frozenset type is described in :ref:`types-set`. |
| 477 | |
| 478 | For other containers see the built in :class:`dict`, :class:`list`, and |
| 479 | :class:`tuple` classes, and the :mod:`collections` module. |
| 480 | |
Georg Brandl | 116aa62 | 2007-08-15 14:28:22 +0000 | [diff] [blame] | 481 | |
| 482 | .. function:: getattr(object, name[, default]) |
| 483 | |
| 484 | Return the value of the named attributed of *object*. *name* must be a string. |
| 485 | If the string is the name of one of the object's attributes, the result is the |
| 486 | value of that attribute. For example, ``getattr(x, 'foobar')`` is equivalent to |
| 487 | ``x.foobar``. If the named attribute does not exist, *default* is returned if |
| 488 | provided, otherwise :exc:`AttributeError` is raised. |
| 489 | |
| 490 | |
| 491 | .. function:: globals() |
| 492 | |
| 493 | Return a dictionary representing the current global symbol table. This is always |
| 494 | the dictionary of the current module (inside a function or method, this is the |
| 495 | module where it is defined, not the module from which it is called). |
| 496 | |
| 497 | |
| 498 | .. function:: hasattr(object, name) |
| 499 | |
| 500 | The arguments are an object and a string. The result is ``True`` if the string |
| 501 | is the name of one of the object's attributes, ``False`` if not. (This is |
| 502 | implemented by calling ``getattr(object, name)`` and seeing whether it raises an |
| 503 | exception or not.) |
| 504 | |
| 505 | |
| 506 | .. function:: hash(object) |
| 507 | |
| 508 | Return the hash value of the object (if it has one). Hash values are integers. |
| 509 | They are used to quickly compare dictionary keys during a dictionary lookup. |
| 510 | Numeric values that compare equal have the same hash value (even if they are of |
| 511 | different types, as is the case for 1 and 1.0). |
| 512 | |
| 513 | |
| 514 | .. function:: help([object]) |
| 515 | |
| 516 | Invoke the built-in help system. (This function is intended for interactive |
| 517 | use.) If no argument is given, the interactive help system starts on the |
| 518 | interpreter console. If the argument is a string, then the string is looked up |
| 519 | as the name of a module, function, class, method, keyword, or documentation |
| 520 | topic, and a help page is printed on the console. If the argument is any other |
| 521 | kind of object, a help page on the object is generated. |
| 522 | |
Georg Brandl | 116aa62 | 2007-08-15 14:28:22 +0000 | [diff] [blame] | 523 | |
| 524 | .. function:: hex(x) |
| 525 | |
| 526 | Convert an integer number to a hexadecimal string. The result is a valid Python |
| 527 | expression. If *x* is not a Python :class:`int` object, it has to define an |
| 528 | :meth:`__index__` method that returns an integer. |
| 529 | |
Georg Brandl | 116aa62 | 2007-08-15 14:28:22 +0000 | [diff] [blame] | 530 | |
| 531 | .. function:: id(object) |
| 532 | |
Georg Brandl | ba956ae | 2007-11-29 17:24:34 +0000 | [diff] [blame] | 533 | Return the "identity" of an object. This is an integer which |
Georg Brandl | 116aa62 | 2007-08-15 14:28:22 +0000 | [diff] [blame] | 534 | is guaranteed to be unique and constant for this object during its lifetime. |
| 535 | Two objects with non-overlapping lifetimes may have the same :func:`id` value. |
| 536 | (Implementation note: this is the address of the object.) |
| 537 | |
| 538 | |
Georg Brandl | c090298 | 2007-09-12 21:29:27 +0000 | [diff] [blame] | 539 | .. function:: input([prompt]) |
| 540 | |
| 541 | If the *prompt* argument is present, it is written to standard output without |
| 542 | a trailing newline. The function then reads a line from input, converts it |
| 543 | to a string (stripping a trailing newline), and returns that. When EOF is |
| 544 | read, :exc:`EOFError` is raised. Example:: |
| 545 | |
Georg Brandl | 7b46942 | 2007-09-12 21:32:27 +0000 | [diff] [blame] | 546 | >>> s = input('--> ') |
Georg Brandl | c090298 | 2007-09-12 21:29:27 +0000 | [diff] [blame] | 547 | --> Monty Python's Flying Circus |
| 548 | >>> s |
| 549 | "Monty Python's Flying Circus" |
| 550 | |
Georg Brandl | 7b46942 | 2007-09-12 21:32:27 +0000 | [diff] [blame] | 551 | 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] | 552 | to provide elaborate line editing and history features. |
| 553 | |
| 554 | |
Georg Brandl | 116aa62 | 2007-08-15 14:28:22 +0000 | [diff] [blame] | 555 | .. function:: int([x[, radix]]) |
| 556 | |
| 557 | Convert a string or number to an integer. If the argument is a string, it |
Georg Brandl | 9afde1c | 2007-11-01 20:32:30 +0000 | [diff] [blame] | 558 | must contain a possibly signed number of arbitrary size, possibly embedded in |
| 559 | whitespace. The *radix* parameter gives the base for the conversion (which |
| 560 | is 10 by default) and may be any integer in the range [2, 36], or zero. If |
| 561 | *radix* is zero, the interpretation is the same as for integer literals. If |
| 562 | *radix* is specified and *x* is not a string, :exc:`TypeError` is raised. |
| 563 | Otherwise, the argument may be another integer, a floating point number or |
| 564 | any other object that has an :meth:`__int__` method. Conversion of floating |
| 565 | point numbers to integers truncates (towards zero). If no arguments are |
| 566 | given, returns ``0``. |
Georg Brandl | 116aa62 | 2007-08-15 14:28:22 +0000 | [diff] [blame] | 567 | |
| 568 | The integer type is described in :ref:`typesnumeric`. |
| 569 | |
| 570 | |
| 571 | .. function:: isinstance(object, classinfo) |
| 572 | |
Georg Brandl | 85eb8c1 | 2007-08-31 16:33:38 +0000 | [diff] [blame] | 573 | Return true if the *object* argument is an instance of the *classinfo* |
| 574 | argument, or of a (direct or indirect) subclass thereof. If *object* is not |
| 575 | an object of the given type, the function always returns false. If |
| 576 | *classinfo* is not a class (type object), it may be a tuple of type objects, |
| 577 | or may recursively contain other such tuples (other sequence types are not |
| 578 | accepted). If *classinfo* is not a type or tuple of types and such tuples, |
| 579 | a :exc:`TypeError` exception is raised. |
Georg Brandl | 116aa62 | 2007-08-15 14:28:22 +0000 | [diff] [blame] | 580 | |
Georg Brandl | 116aa62 | 2007-08-15 14:28:22 +0000 | [diff] [blame] | 581 | |
| 582 | .. function:: issubclass(class, classinfo) |
| 583 | |
| 584 | Return true if *class* is a subclass (direct or indirect) of *classinfo*. A |
| 585 | class is considered a subclass of itself. *classinfo* may be a tuple of class |
| 586 | objects, in which case every entry in *classinfo* will be checked. In any other |
| 587 | case, a :exc:`TypeError` exception is raised. |
| 588 | |
Georg Brandl | 116aa62 | 2007-08-15 14:28:22 +0000 | [diff] [blame] | 589 | |
| 590 | .. function:: iter(o[, sentinel]) |
| 591 | |
Georg Brandl | 9afde1c | 2007-11-01 20:32:30 +0000 | [diff] [blame] | 592 | Return an :term:`iterator` object. The first argument is interpreted very differently |
Georg Brandl | 116aa62 | 2007-08-15 14:28:22 +0000 | [diff] [blame] | 593 | depending on the presence of the second argument. Without a second argument, *o* |
| 594 | must be a collection object which supports the iteration protocol (the |
| 595 | :meth:`__iter__` method), or it must support the sequence protocol (the |
| 596 | :meth:`__getitem__` method with integer arguments starting at ``0``). If it |
| 597 | does not support either of those protocols, :exc:`TypeError` is raised. If the |
| 598 | second argument, *sentinel*, is given, then *o* must be a callable object. The |
| 599 | iterator created in this case will call *o* with no arguments for each call to |
| 600 | its :meth:`__next__` method; if the value returned is equal to *sentinel*, |
| 601 | :exc:`StopIteration` will be raised, otherwise the value will be returned. |
| 602 | |
Georg Brandl | 116aa62 | 2007-08-15 14:28:22 +0000 | [diff] [blame] | 603 | |
| 604 | .. function:: len(s) |
| 605 | |
| 606 | Return the length (the number of items) of an object. The argument may be a |
| 607 | sequence (string, tuple or list) or a mapping (dictionary). |
| 608 | |
| 609 | |
| 610 | .. function:: list([iterable]) |
| 611 | |
| 612 | Return a list whose items are the same and in the same order as *iterable*'s |
| 613 | items. *iterable* may be either a sequence, a container that supports |
| 614 | iteration, or an iterator object. If *iterable* is already a list, a copy is |
| 615 | made and returned, similar to ``iterable[:]``. For instance, ``list('abc')`` |
| 616 | returns ``['a', 'b', 'c']`` and ``list( (1, 2, 3) )`` returns ``[1, 2, 3]``. If |
| 617 | no argument is given, returns a new empty list, ``[]``. |
| 618 | |
| 619 | :class:`list` is a mutable sequence type, as documented in |
| 620 | :ref:`typesseq`. For other containers see the built in :class:`dict`, |
| 621 | :class:`set`, and :class:`tuple` classes, and the :mod:`collections` module. |
| 622 | |
| 623 | |
| 624 | .. function:: locals() |
| 625 | |
| 626 | Update and return a dictionary representing the current local symbol table. |
| 627 | |
| 628 | .. warning:: |
| 629 | |
| 630 | The contents of this dictionary should not be modified; changes may not affect |
| 631 | the values of local variables used by the interpreter. |
| 632 | |
| 633 | Free variables are returned by *locals* when it is called in a function block. |
| 634 | Modifications of free variables may not affect the values used by the |
| 635 | interpreter. Free variables are not returned in class blocks. |
| 636 | |
| 637 | |
| 638 | .. function:: map(function, iterable, ...) |
| 639 | |
Georg Brandl | 952aea2 | 2007-09-04 17:50:40 +0000 | [diff] [blame] | 640 | Return an iterator that applies *function* to every item of *iterable*, |
| 641 | yielding the results. If additional *iterable* arguments are passed, |
| 642 | *function* must take that many arguments and is applied to the items from all |
| 643 | iterables in parallel. If one iterable is shorter than another it is assumed |
| 644 | to be extended with ``None`` items. If *function* is ``None``, the identity |
| 645 | function is assumed; if there are multiple arguments, :func:`map` returns a |
| 646 | list consisting of tuples containing the corresponding items from all |
| 647 | iterables (a kind of transpose operation). The *iterable* arguments may be a |
| 648 | sequence or any iterable object; the result is always a list. |
| 649 | |
| 650 | Note that for only one *iterable* argument, ``map(function, iterable)`` is |
| 651 | equivalent to the generator expression ``(function(item) for item in |
| 652 | iterable)`` if *function* is not ``None``. |
Georg Brandl | 116aa62 | 2007-08-15 14:28:22 +0000 | [diff] [blame] | 653 | |
| 654 | |
Georg Brandl | 55ac8f0 | 2007-09-01 13:51:09 +0000 | [diff] [blame] | 655 | .. function:: max(iterable[, args...], *[, key]) |
Georg Brandl | 116aa62 | 2007-08-15 14:28:22 +0000 | [diff] [blame] | 656 | |
| 657 | With a single argument *iterable*, return the largest item of a non-empty |
| 658 | iterable (such as a string, tuple or list). With more than one argument, return |
| 659 | the largest of the arguments. |
| 660 | |
Georg Brandl | 55ac8f0 | 2007-09-01 13:51:09 +0000 | [diff] [blame] | 661 | The optional keyword-only *key* argument specifies a one-argument ordering |
| 662 | function like that used for :meth:`list.sort`. |
Georg Brandl | 116aa62 | 2007-08-15 14:28:22 +0000 | [diff] [blame] | 663 | |
| 664 | |
Georg Brandl | 85eb8c1 | 2007-08-31 16:33:38 +0000 | [diff] [blame] | 665 | .. function:: memoryview(obj) |
| 666 | |
| 667 | Return a "memory view" object created from the given argument. |
| 668 | |
| 669 | XXX: To be documented. |
| 670 | |
| 671 | |
Georg Brandl | 55ac8f0 | 2007-09-01 13:51:09 +0000 | [diff] [blame] | 672 | .. function:: min(iterable[, args...], *[, key]) |
Georg Brandl | 116aa62 | 2007-08-15 14:28:22 +0000 | [diff] [blame] | 673 | |
| 674 | With a single argument *iterable*, return the smallest item of a non-empty |
| 675 | iterable (such as a string, tuple or list). With more than one argument, return |
| 676 | the smallest of the arguments. |
| 677 | |
Georg Brandl | 55ac8f0 | 2007-09-01 13:51:09 +0000 | [diff] [blame] | 678 | The optional keyword-only *key* argument specifies a one-argument ordering |
| 679 | function like that used for :meth:`list.sort`. |
Georg Brandl | 116aa62 | 2007-08-15 14:28:22 +0000 | [diff] [blame] | 680 | |
| 681 | |
| 682 | .. function:: next(iterator[, default]) |
| 683 | |
| 684 | Retrieve the next item from the *iterable* by calling its :meth:`__next__` |
| 685 | method. If *default* is given, it is returned if the iterator is exhausted, |
| 686 | otherwise :exc:`StopIteration` is raised. |
| 687 | |
| 688 | |
| 689 | .. function:: object() |
| 690 | |
Georg Brandl | 85eb8c1 | 2007-08-31 16:33:38 +0000 | [diff] [blame] | 691 | 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] | 692 | It has the methods that are common to all instances of Python classes. This |
| 693 | function does not accept any arguments. |
Georg Brandl | 85eb8c1 | 2007-08-31 16:33:38 +0000 | [diff] [blame] | 694 | |
| 695 | .. note:: |
| 696 | |
| 697 | :class:`object` does *not* have a :attr:`__dict__`, so you can't assign |
| 698 | arbitrary attributes to an instance of the :class:`object` class. |
Georg Brandl | 116aa62 | 2007-08-15 14:28:22 +0000 | [diff] [blame] | 699 | |
Georg Brandl | 116aa62 | 2007-08-15 14:28:22 +0000 | [diff] [blame] | 700 | |
| 701 | .. function:: oct(x) |
| 702 | |
| 703 | Convert an integer number to an octal string. The result is a valid Python |
| 704 | expression. If *x* is not a Python :class:`int` object, it has to define an |
| 705 | :meth:`__index__` method that returns an integer. |
| 706 | |
Georg Brandl | 116aa62 | 2007-08-15 14:28:22 +0000 | [diff] [blame] | 707 | |
| 708 | .. function:: open(filename[, mode[, bufsize]]) |
| 709 | |
| 710 | Open a file, returning an object of the :class:`file` type described in |
| 711 | section :ref:`bltin-file-objects`. If the file cannot be opened, |
| 712 | :exc:`IOError` is raised. When opening a file, it's preferable to use |
| 713 | :func:`open` instead of invoking the :class:`file` constructor directly. |
| 714 | |
| 715 | The first two arguments are the same as for ``stdio``'s :cfunc:`fopen`: |
Skip Montanaro | 1c63960 | 2007-09-23 19:49:54 +0000 | [diff] [blame] | 716 | *filename* is the file name to be opened, and *mode* is a string |
| 717 | indicating how the file is to be opened. |
Georg Brandl | 116aa62 | 2007-08-15 14:28:22 +0000 | [diff] [blame] | 718 | |
Skip Montanaro | 1c63960 | 2007-09-23 19:49:54 +0000 | [diff] [blame] | 719 | The most commonly-used values of *mode* are ``'r'`` for reading, ``'w'`` |
| 720 | for writing (truncating the file if it already exists), and ``'a'`` for |
| 721 | appending (which on *some* Unix systems means that *all* writes append to |
| 722 | the end of the file regardless of the current seek position). If *mode* |
Skip Montanaro | 4d8c193 | 2007-09-23 21:13:45 +0000 | [diff] [blame] | 723 | is omitted, it defaults to ``'r'``. See below for more possible values |
| 724 | of *mode*. |
Skip Montanaro | 1c63960 | 2007-09-23 19:49:54 +0000 | [diff] [blame] | 725 | |
Skip Montanaro | 4d8c193 | 2007-09-23 21:13:45 +0000 | [diff] [blame] | 726 | Python distinguishes between files opened in binary and text modes, even |
| 727 | when the underlying operating system doesn't. Files opened in binary |
| 728 | mode (appending ``'b'`` to the *mode* argument to :func:``open``) return |
| 729 | contents as bytes objects without any decoding. In text mode (the |
| 730 | default, or when ``'t'`` is appended to the *mode* argument) the contents |
| 731 | of the file are returned as strings, the bytes having been first decoded |
| 732 | using the encoding specified by :func:`sys.getfilesystemencoding`. |
Georg Brandl | 116aa62 | 2007-08-15 14:28:22 +0000 | [diff] [blame] | 733 | |
| 734 | .. index:: |
| 735 | single: line-buffered I/O |
| 736 | single: unbuffered I/O |
| 737 | single: buffer size, I/O |
| 738 | single: I/O control; buffering |
Skip Montanaro | 4d8c193 | 2007-09-23 21:13:45 +0000 | [diff] [blame] | 739 | single: binary mode |
| 740 | single: text mode |
| 741 | module: sys |
Georg Brandl | 116aa62 | 2007-08-15 14:28:22 +0000 | [diff] [blame] | 742 | |
Skip Montanaro | 1c63960 | 2007-09-23 19:49:54 +0000 | [diff] [blame] | 743 | The optional *bufsize* argument specifies the file's desired buffer size: |
| 744 | 0 means unbuffered, 1 means line buffered, any other positive value means |
| 745 | use a buffer of (approximately) that size. A negative *bufsize* means to |
| 746 | use the system default, which is usually line buffered for tty devices |
| 747 | and fully buffered for other files. If omitted, the system default is |
| 748 | used. [#]_ |
Georg Brandl | 116aa62 | 2007-08-15 14:28:22 +0000 | [diff] [blame] | 749 | |
Skip Montanaro | 1c63960 | 2007-09-23 19:49:54 +0000 | [diff] [blame] | 750 | Modes ``'r+'``, ``'w+'`` and ``'a+'`` open the file for updating (note |
Skip Montanaro | 4d8c193 | 2007-09-23 21:13:45 +0000 | [diff] [blame] | 751 | that ``'w+'`` truncates the file). |
Georg Brandl | 116aa62 | 2007-08-15 14:28:22 +0000 | [diff] [blame] | 752 | |
Skip Montanaro | 4d8c193 | 2007-09-23 21:13:45 +0000 | [diff] [blame] | 753 | When a file is opened in text mode it is also opened in universal |
| 754 | newlines mode. Unlike earlier versions of Python it's no longer |
| 755 | necessary to add a ``'U'`` value to the *mode* argument to enable this |
| 756 | mode. Consequently, in files opened in text mode lines may be terminated |
| 757 | with ``'\n'``, ``'\r'``, or ``'\r\n'``. All three external |
| 758 | representations are seen as ``'\n'`` by the Python program. File objects |
| 759 | opened in text mode also have a :attr:`newlines` attribute which has a |
| 760 | value of ``None`` (if no newlines have been seen yet), ``'\n'``, |
Skip Montanaro | 1c63960 | 2007-09-23 19:49:54 +0000 | [diff] [blame] | 761 | ``'\r'``, ``'\r\n'``, or a tuple containing all the newline types seen. |
Georg Brandl | 116aa62 | 2007-08-15 14:28:22 +0000 | [diff] [blame] | 762 | |
Guido van Rossum | 2cc30da | 2007-11-02 23:46:40 +0000 | [diff] [blame] | 763 | Python provides many file handling modules including |
| 764 | :mod:`fileinput`, :mod:`os`, :mod:`os.path`, :mod:`tempfile`, and |
| 765 | :mod:`shutil`. |
Georg Brandl | 116aa62 | 2007-08-15 14:28:22 +0000 | [diff] [blame] | 766 | |
| 767 | .. function:: ord(c) |
| 768 | |
| 769 | Given a string of length one, return an integer representing the Unicode code |
| 770 | point of the character when the argument is a unicode object, or the value of |
| 771 | the byte when the argument is an 8-bit string. For example, ``ord('a')`` returns |
| 772 | the integer ``97``, ``ord(u'\u2020')`` returns ``8224``. This is the inverse of |
| 773 | :func:`chr` for 8-bit strings and of :func:`unichr` for unicode objects. If a |
| 774 | unicode argument is given and Python was built with UCS2 Unicode, then the |
| 775 | character's code point must be in the range [0..65535] inclusive; otherwise the |
| 776 | string length is two, and a :exc:`TypeError` will be raised. |
| 777 | |
| 778 | |
| 779 | .. function:: pow(x, y[, z]) |
| 780 | |
| 781 | Return *x* to the power *y*; if *z* is present, return *x* to the power *y*, |
| 782 | modulo *z* (computed more efficiently than ``pow(x, y) % z``). The two-argument |
| 783 | form ``pow(x, y)`` is equivalent to using the power operator: ``x**y``. |
| 784 | |
| 785 | The arguments must have numeric types. With mixed operand types, the coercion |
Georg Brandl | ba956ae | 2007-11-29 17:24:34 +0000 | [diff] [blame] | 786 | rules for binary arithmetic operators apply. For :class:`int` operands, the |
Georg Brandl | 116aa62 | 2007-08-15 14:28:22 +0000 | [diff] [blame] | 787 | result has the same type as the operands (after coercion) unless the second |
| 788 | argument is negative; in that case, all arguments are converted to float and a |
| 789 | float result is delivered. For example, ``10**2`` returns ``100``, but |
| 790 | ``10**-2`` returns ``0.01``. (This last feature was added in Python 2.2. In |
| 791 | Python 2.1 and before, if both arguments were of integer types and the second |
| 792 | argument was negative, an exception was raised.) If the second argument is |
| 793 | negative, the third argument must be omitted. If *z* is present, *x* and *y* |
| 794 | must be of integer types, and *y* must be non-negative. (This restriction was |
| 795 | added in Python 2.2. In Python 2.1 and before, floating 3-argument ``pow()`` |
| 796 | returned platform-dependent results depending on floating-point rounding |
| 797 | accidents.) |
| 798 | |
| 799 | |
| 800 | .. function:: property([fget[, fset[, fdel[, doc]]]]) |
| 801 | |
Georg Brandl | 85eb8c1 | 2007-08-31 16:33:38 +0000 | [diff] [blame] | 802 | Return a property attribute. |
Georg Brandl | 116aa62 | 2007-08-15 14:28:22 +0000 | [diff] [blame] | 803 | |
| 804 | *fget* is a function for getting an attribute value, likewise *fset* is a |
| 805 | function for setting, and *fdel* a function for del'ing, an attribute. Typical |
| 806 | use is to define a managed attribute x:: |
| 807 | |
| 808 | class C(object): |
| 809 | def __init__(self): self._x = None |
| 810 | def getx(self): return self._x |
| 811 | def setx(self, value): self._x = value |
| 812 | def delx(self): del self._x |
| 813 | x = property(getx, setx, delx, "I'm the 'x' property.") |
| 814 | |
| 815 | If given, *doc* will be the docstring of the property attribute. Otherwise, the |
| 816 | property will copy *fget*'s docstring (if it exists). This makes it possible to |
| 817 | create read-only properties easily using :func:`property` as a decorator:: |
| 818 | |
| 819 | class Parrot(object): |
| 820 | def __init__(self): |
| 821 | self._voltage = 100000 |
| 822 | |
| 823 | @property |
| 824 | def voltage(self): |
| 825 | """Get the current voltage.""" |
| 826 | return self._voltage |
| 827 | |
| 828 | turns the :meth:`voltage` method into a "getter" for a read-only attribute with |
| 829 | the same name. |
| 830 | |
Georg Brandl | 116aa62 | 2007-08-15 14:28:22 +0000 | [diff] [blame] | 831 | |
Georg Brandl | 952aea2 | 2007-09-04 17:50:40 +0000 | [diff] [blame] | 832 | .. XXX does accept objects with __index__ too |
Georg Brandl | 116aa62 | 2007-08-15 14:28:22 +0000 | [diff] [blame] | 833 | .. function:: range([start,] stop[, step]) |
| 834 | |
Georg Brandl | 952aea2 | 2007-09-04 17:50:40 +0000 | [diff] [blame] | 835 | This is a versatile function to create iterators containing arithmetic |
Georg Brandl | 116aa62 | 2007-08-15 14:28:22 +0000 | [diff] [blame] | 836 | progressions. It is most often used in :keyword:`for` loops. The arguments |
Georg Brandl | 952aea2 | 2007-09-04 17:50:40 +0000 | [diff] [blame] | 837 | must be integers. If the *step* argument is omitted, it defaults to ``1``. |
| 838 | If the *start* argument is omitted, it defaults to ``0``. The full form |
| 839 | returns an iterator of plain integers ``[start, start + step, start + 2 * |
| 840 | step, ...]``. If *step* is positive, the last element is the largest ``start |
| 841 | + i * step`` less than *stop*; if *step* is negative, the last element is the |
| 842 | smallest ``start + i * step`` greater than *stop*. *step* must not be zero |
| 843 | (or else :exc:`ValueError` is raised). Example:: |
Georg Brandl | 116aa62 | 2007-08-15 14:28:22 +0000 | [diff] [blame] | 844 | |
| 845 | >>> list(range(10)) |
| 846 | [0, 1, 2, 3, 4, 5, 6, 7, 8, 9] |
| 847 | >>> list(range(1, 11)) |
| 848 | [1, 2, 3, 4, 5, 6, 7, 8, 9, 10] |
| 849 | >>> list(range(0, 30, 5)) |
| 850 | [0, 5, 10, 15, 20, 25] |
| 851 | >>> list(range(0, 10, 3)) |
| 852 | [0, 3, 6, 9] |
| 853 | >>> list(range(0, -10, -1)) |
| 854 | [0, -1, -2, -3, -4, -5, -6, -7, -8, -9] |
| 855 | >>> list(range(0)) |
| 856 | [] |
| 857 | >>> list(range(1, 0)) |
| 858 | [] |
| 859 | |
| 860 | |
| 861 | .. function:: repr(object) |
| 862 | |
| 863 | Return a string containing a printable representation of an object. This is the |
| 864 | same value yielded by conversions (reverse quotes). It is sometimes useful to be |
| 865 | able to access this operation as an ordinary function. For many types, this |
| 866 | function makes an attempt to return a string that would yield an object with the |
| 867 | same value when passed to :func:`eval`. |
| 868 | |
| 869 | |
| 870 | .. function:: reversed(seq) |
| 871 | |
Georg Brandl | 9afde1c | 2007-11-01 20:32:30 +0000 | [diff] [blame] | 872 | Return a reverse :term:`iterator`. *seq* must be an object which supports |
| 873 | the sequence protocol (the :meth:`__len__` method and the :meth:`__getitem__` |
| 874 | method with integer arguments starting at ``0``). |
Georg Brandl | 116aa62 | 2007-08-15 14:28:22 +0000 | [diff] [blame] | 875 | |
Georg Brandl | 116aa62 | 2007-08-15 14:28:22 +0000 | [diff] [blame] | 876 | |
| 877 | .. function:: round(x[, n]) |
| 878 | |
| 879 | Return the floating point value *x* rounded to *n* digits after the decimal |
| 880 | point. If *n* is omitted, it defaults to zero. The result is a floating point |
| 881 | number. Values are rounded to the closest multiple of 10 to the power minus |
| 882 | *n*; if two multiples are equally close, rounding is done away from 0 (so. for |
| 883 | example, ``round(0.5)`` is ``1.0`` and ``round(-0.5)`` is ``-1.0``). |
| 884 | |
| 885 | |
| 886 | .. function:: set([iterable]) |
| 887 | :noindex: |
| 888 | |
| 889 | Return a new set, optionally with elements are taken from *iterable*. |
| 890 | The set type is described in :ref:`types-set`. |
| 891 | |
| 892 | For other containers see the built in :class:`dict`, :class:`list`, and |
| 893 | :class:`tuple` classes, and the :mod:`collections` module. |
| 894 | |
Georg Brandl | 116aa62 | 2007-08-15 14:28:22 +0000 | [diff] [blame] | 895 | |
| 896 | .. function:: setattr(object, name, value) |
| 897 | |
| 898 | This is the counterpart of :func:`getattr`. The arguments are an object, a |
| 899 | string and an arbitrary value. The string may name an existing attribute or a |
| 900 | new attribute. The function assigns the value to the attribute, provided the |
| 901 | object allows it. For example, ``setattr(x, 'foobar', 123)`` is equivalent to |
| 902 | ``x.foobar = 123``. |
| 903 | |
| 904 | |
| 905 | .. function:: slice([start,] stop[, step]) |
| 906 | |
| 907 | .. index:: single: Numerical Python |
| 908 | |
| 909 | Return a slice object representing the set of indices specified by |
| 910 | ``range(start, stop, step)``. The *start* and *step* arguments default to |
| 911 | ``None``. Slice objects have read-only data attributes :attr:`start`, |
| 912 | :attr:`stop` and :attr:`step` which merely return the argument values (or their |
| 913 | default). They have no other explicit functionality; however they are used by |
| 914 | Numerical Python and other third party extensions. Slice objects are also |
| 915 | generated when extended indexing syntax is used. For example: |
| 916 | ``a[start:stop:step]`` or ``a[start:stop, i]``. |
| 917 | |
| 918 | |
| 919 | .. function:: sorted(iterable[, cmp[, key[, reverse]]]) |
| 920 | |
| 921 | Return a new sorted list from the items in *iterable*. |
| 922 | |
| 923 | The optional arguments *cmp*, *key*, and *reverse* have the same meaning as |
| 924 | those for the :meth:`list.sort` method (described in section |
| 925 | :ref:`typesseq-mutable`). |
| 926 | |
| 927 | *cmp* specifies a custom comparison function of two arguments (iterable |
| 928 | elements) which should return a negative, zero or positive number depending on |
| 929 | whether the first argument is considered smaller than, equal to, or larger than |
| 930 | the second argument: ``cmp=lambda x,y: cmp(x.lower(), y.lower())`` |
| 931 | |
| 932 | *key* specifies a function of one argument that is used to extract a comparison |
| 933 | key from each list element: ``key=str.lower`` |
| 934 | |
| 935 | *reverse* is a boolean value. If set to ``True``, then the list elements are |
| 936 | sorted as if each comparison were reversed. |
| 937 | |
| 938 | In general, the *key* and *reverse* conversion processes are much faster than |
| 939 | specifying an equivalent *cmp* function. This is because *cmp* is called |
| 940 | multiple times for each list element while *key* and *reverse* touch each |
| 941 | element only once. |
| 942 | |
Georg Brandl | 116aa62 | 2007-08-15 14:28:22 +0000 | [diff] [blame] | 943 | |
| 944 | .. function:: staticmethod(function) |
| 945 | |
| 946 | Return a static method for *function*. |
| 947 | |
| 948 | A static method does not receive an implicit first argument. To declare a static |
| 949 | method, use this idiom:: |
| 950 | |
| 951 | class C: |
| 952 | @staticmethod |
| 953 | def f(arg1, arg2, ...): ... |
| 954 | |
| 955 | The ``@staticmethod`` form is a function decorator -- see the description of |
| 956 | function definitions in :ref:`function` for details. |
| 957 | |
| 958 | It can be called either on the class (such as ``C.f()``) or on an instance (such |
| 959 | as ``C().f()``). The instance is ignored except for its class. |
| 960 | |
| 961 | Static methods in Python are similar to those found in Java or C++. For a more |
| 962 | advanced concept, see :func:`classmethod` in this section. |
| 963 | |
| 964 | For more information on static methods, consult the documentation on the |
| 965 | standard type hierarchy in :ref:`types`. |
| 966 | |
Georg Brandl | 116aa62 | 2007-08-15 14:28:22 +0000 | [diff] [blame] | 967 | |
| 968 | .. function:: str([object[, encoding[, errors]]]) |
| 969 | |
| 970 | Return a string version of an object, using one of the following modes: |
| 971 | |
| 972 | If *encoding* and/or *errors* are given, :func:`str` will decode the |
| 973 | *object* which can either be a byte string or a character buffer using |
| 974 | the codec for *encoding*. The *encoding* parameter is a string giving |
| 975 | the name of an encoding; if the encoding is not known, :exc:`LookupError` |
| 976 | is raised. Error handling is done according to *errors*; this specifies the |
| 977 | treatment of characters which are invalid in the input encoding. If |
| 978 | *errors* is ``'strict'`` (the default), a :exc:`ValueError` is raised on |
| 979 | errors, while a value of ``'ignore'`` causes errors to be silently ignored, |
| 980 | and a value of ``'replace'`` causes the official Unicode replacement character, |
| 981 | U+FFFD, to be used to replace input characters which cannot be decoded. |
| 982 | See also the :mod:`codecs` module. |
| 983 | |
| 984 | When only *object* is given, this returns its nicely printable representation. |
| 985 | For strings, this is the string itself. The difference with ``repr(object)`` |
| 986 | is that ``str(object)`` does not always attempt to return a string that is |
| 987 | acceptable to :func:`eval`; its goal is to return a printable string. |
| 988 | With no arguments, this returns the empty string. |
| 989 | |
| 990 | Objects can specify what ``str(object)`` returns by defining a :meth:`__str__` |
| 991 | special method. |
| 992 | |
| 993 | For more information on strings see :ref:`typesseq` which describes sequence |
| 994 | functionality (strings are sequences), and also the string-specific methods |
Georg Brandl | 4b49131 | 2007-08-31 09:22:56 +0000 | [diff] [blame] | 995 | described in the :ref:`string-methods` section. To output formatted strings, |
| 996 | see the :ref:`string-formatting` section. In addition see the |
| 997 | :ref:`stringservices` section. |
Georg Brandl | 116aa62 | 2007-08-15 14:28:22 +0000 | [diff] [blame] | 998 | |
| 999 | |
| 1000 | .. function:: sum(iterable[, start]) |
| 1001 | |
| 1002 | Sums *start* and the items of an *iterable* from left to right and returns the |
| 1003 | total. *start* defaults to ``0``. The *iterable*'s items are normally numbers, |
| 1004 | and are not allowed to be strings. The fast, correct way to concatenate a |
| 1005 | sequence of strings is by calling ``''.join(sequence)``. |
| 1006 | |
Georg Brandl | 116aa62 | 2007-08-15 14:28:22 +0000 | [diff] [blame] | 1007 | |
| 1008 | .. function:: super(type[, object-or-type]) |
| 1009 | |
Georg Brandl | 85eb8c1 | 2007-08-31 16:33:38 +0000 | [diff] [blame] | 1010 | .. XXX need to document PEP "new super" |
| 1011 | |
Georg Brandl | 116aa62 | 2007-08-15 14:28:22 +0000 | [diff] [blame] | 1012 | Return the superclass of *type*. If the second argument is omitted the super |
| 1013 | object returned is unbound. If the second argument is an object, |
| 1014 | ``isinstance(obj, type)`` must be true. If the second argument is a type, |
Georg Brandl | 85eb8c1 | 2007-08-31 16:33:38 +0000 | [diff] [blame] | 1015 | ``issubclass(type2, type)`` must be true. |
Georg Brandl | 116aa62 | 2007-08-15 14:28:22 +0000 | [diff] [blame] | 1016 | |
| 1017 | A typical use for calling a cooperative superclass method is:: |
| 1018 | |
| 1019 | class C(B): |
| 1020 | def meth(self, arg): |
| 1021 | super(C, self).meth(arg) |
| 1022 | |
| 1023 | Note that :func:`super` is implemented as part of the binding process for |
| 1024 | explicit dotted attribute lookups such as ``super(C, self).__getitem__(name)``. |
| 1025 | Accordingly, :func:`super` is undefined for implicit lookups using statements or |
| 1026 | operators such as ``super(C, self)[name]``. |
| 1027 | |
Georg Brandl | 116aa62 | 2007-08-15 14:28:22 +0000 | [diff] [blame] | 1028 | |
| 1029 | .. function:: tuple([iterable]) |
| 1030 | |
| 1031 | Return a tuple whose items are the same and in the same order as *iterable*'s |
| 1032 | items. *iterable* may be a sequence, a container that supports iteration, or an |
| 1033 | iterator object. If *iterable* is already a tuple, it is returned unchanged. |
| 1034 | For instance, ``tuple('abc')`` returns ``('a', 'b', 'c')`` and ``tuple([1, 2, |
| 1035 | 3])`` returns ``(1, 2, 3)``. If no argument is given, returns a new empty |
| 1036 | tuple, ``()``. |
| 1037 | |
| 1038 | :class:`tuple` is an immutable sequence type, as documented in |
| 1039 | :ref:`typesseq`. For other containers see the built in :class:`dict`, |
| 1040 | :class:`list`, and :class:`set` classes, and the :mod:`collections` module. |
| 1041 | |
| 1042 | |
| 1043 | .. function:: type(object) |
| 1044 | |
| 1045 | .. index:: object: type |
| 1046 | |
Georg Brandl | 85eb8c1 | 2007-08-31 16:33:38 +0000 | [diff] [blame] | 1047 | Return the type of an *object*. The return value is a type object and |
| 1048 | generally the same object as returned by ``object.__class__``. |
Georg Brandl | 116aa62 | 2007-08-15 14:28:22 +0000 | [diff] [blame] | 1049 | |
Georg Brandl | 85eb8c1 | 2007-08-31 16:33:38 +0000 | [diff] [blame] | 1050 | The :func:`isinstance` built-in function is recommended for testing the type |
| 1051 | of an object, because it takes subclasses into account. |
| 1052 | |
| 1053 | With three arguments, :func:`type` functions as a constructor as detailed |
| 1054 | below. |
Georg Brandl | 116aa62 | 2007-08-15 14:28:22 +0000 | [diff] [blame] | 1055 | |
| 1056 | |
| 1057 | .. function:: type(name, bases, dict) |
| 1058 | :noindex: |
| 1059 | |
| 1060 | Return a new type object. This is essentially a dynamic form of the |
Georg Brandl | 85eb8c1 | 2007-08-31 16:33:38 +0000 | [diff] [blame] | 1061 | :keyword:`class` statement. The *name* string is the class name and becomes |
| 1062 | the :attr:`__name__` attribute; the *bases* tuple itemizes the base classes |
| 1063 | and becomes the :attr:`__bases__` attribute; and the *dict* dictionary is the |
| 1064 | namespace containing definitions for class body and becomes the |
| 1065 | :attr:`__dict__` attribute. For example, the following two statements create |
| 1066 | identical :class:`type` objects:: |
Georg Brandl | 116aa62 | 2007-08-15 14:28:22 +0000 | [diff] [blame] | 1067 | |
| 1068 | >>> class X(object): |
| 1069 | ... a = 1 |
| 1070 | ... |
| 1071 | >>> X = type('X', (object,), dict(a=1)) |
| 1072 | |
Georg Brandl | 116aa62 | 2007-08-15 14:28:22 +0000 | [diff] [blame] | 1073 | |
| 1074 | .. function:: vars([object]) |
| 1075 | |
| 1076 | Without arguments, return a dictionary corresponding to the current local symbol |
| 1077 | table. With a module, class or class instance object as argument (or anything |
| 1078 | else that has a :attr:`__dict__` attribute), returns a dictionary corresponding |
| 1079 | to the object's symbol table. The returned dictionary should not be modified: |
| 1080 | the effects on the corresponding symbol table are undefined. [#]_ |
| 1081 | |
| 1082 | |
| 1083 | .. function:: zip([iterable, ...]) |
| 1084 | |
Georg Brandl | 952aea2 | 2007-09-04 17:50:40 +0000 | [diff] [blame] | 1085 | This function returns an iterator of tuples, where the *i*-th tuple contains |
| 1086 | the *i*-th element from each of the argument sequences or iterables. The |
| 1087 | iterator stops when the shortest argument sequence is exhausted. When there |
| 1088 | are multiple arguments which are all of the same length, :func:`zip` is |
| 1089 | similar to :func:`map` with an initial argument of ``None``. With a single |
| 1090 | sequence argument, it returns an iterator of 1-tuples. With no arguments, it |
| 1091 | returns an empty iterator. |
Georg Brandl | 116aa62 | 2007-08-15 14:28:22 +0000 | [diff] [blame] | 1092 | |
Georg Brandl | 116aa62 | 2007-08-15 14:28:22 +0000 | [diff] [blame] | 1093 | |
Georg Brandl | 116aa62 | 2007-08-15 14:28:22 +0000 | [diff] [blame] | 1094 | .. rubric:: Footnotes |
| 1095 | |
| 1096 | .. [#] Specifying a buffer size currently has no effect on systems that don't have |
| 1097 | :cfunc:`setvbuf`. The interface to specify the buffer size is not done using a |
| 1098 | method that calls :cfunc:`setvbuf`, because that may dump core when called after |
| 1099 | any I/O has been performed, and there's no reliable way to determine whether |
| 1100 | this is the case. |
| 1101 | |
| 1102 | .. [#] In the current implementation, local variable bindings cannot normally be |
| 1103 | affected this way, but variables retrieved from other scopes (such as modules) |
| 1104 | can be. This may change. |
| 1105 | |