1 \section{Built-in Functions
\label{built-in-funcs
}}
3 The Python interpreter has a number of functions built into it that
4 are always available. They are listed here in alphabetical order.
7 \setindexsubitem{(built-in function)
}
9 \begin{funcdesc
}{__import__
}{name
\optional{, globals
\optional{, locals
\optional{, fromlist
}}}}
10 This function is invoked by the
11 \keyword{import
}\stindex{import
} statement. It mainly
12 exists so that you can replace it with another function that has a
13 compatible interface, in order to change the semantics of the
14 \keyword{import
} statement. For examples of why and how you would do
15 this, see the standard library modules
16 \module{ihooks
}\refstmodindex{ihooks
} and
17 \refmodule{rexec
}\refstmodindex{rexec
}. See also the built-in module
18 \refmodule{imp
}\refbimodindex{imp
}, which defines some useful
19 operations out of which you can build your own
20 \function{__import__()
} function.
22 For example, the statement `
\code{import
} \code{spam
}' results in the
24 \code{__import__('spam',
} \code{globals(),
} \code{locals(),
[])
};
25 the statement
\code{from
} \code{spam.ham import
} \code{eggs
} results
26 in
\code{__import__('spam.ham',
} \code{globals(),
} \code{locals(),
}
28 Note that even though
\code{locals()
} and
\code{['eggs'
]} are passed
29 in as arguments, the
\function{__import__()
} function does not set the
30 local variable named
\code{eggs
}; this is done by subsequent code that
31 is generated for the import statement. (In fact, the standard
32 implementation does not use its
\var{locals
} argument at all, and uses
33 its
\var{globals
} only to determine the package context of the
34 \keyword{import
} statement.)
36 When the
\var{name
} variable is of the form
\code{package.module
},
37 normally, the top-level package (the name up till the first dot) is
38 returned,
\emph{not
} the module named by
\var{name
}. However, when a
39 non-empty
\var{fromlist
} argument is given, the module named by
40 \var{name
} is returned. This is done for compatibility with the
41 bytecode generated for the different kinds of import statement; when
42 using
\samp{import spam.ham.eggs
}, the top-level package
\code{spam
}
43 must be placed in the importing namespace, but when using
\samp{from
44 spam.ham import eggs
}, the
\code{spam.ham
} subpackage must be used to
45 find the
\code{eggs
} variable.
46 As a workaround for this behavior, use
\function{getattr()
} to extract
47 the desired components. For example, you could define the following
54 mod = __import__(name)
55 components = string.split(name, '.')
56 for comp in components
[1:
]:
57 mod = getattr(mod, comp)
63 \begin{funcdesc
}{abs
}{x
}
64 Return the absolute value of a number. The argument may be a plain
65 or long integer or a floating point number. If the argument is a
66 complex number, its magnitude is returned.
69 \begin{funcdesc
}{apply
}{function, args
\optional{, keywords
}}
70 The
\var{function
} argument must be a callable object (a user-defined or
71 built-in function or method, or a class object) and the
\var{args
}
72 argument must be a sequence (if it is not a tuple, the sequence is
73 first converted to a tuple). The
\var{function
} is called with
74 \var{args
} as the argument list; the number of arguments is the the length
75 of the tuple. (This is different from just calling
76 \code{\var{func
}(
\var{args
})
}, since in that case there is always
77 exactly one argument.)
78 If the optional
\var{keywords
} argument is present, it must be a
79 dictionary whose keys are strings. It specifies keyword arguments to
80 be added to the end of the the argument list.
83 \begin{funcdesc
}{buffer
}{object
\optional{, offset
\optional{, size
}}}
84 The
\var{object
} argument must be an object that supports the
85 buffer call interface (such as strings, arrays, and buffers). A new
86 buffer object will be created which references the
\var{object
} argument.
87 The buffer object will be a slice from the beginning of
\var{object
}
88 (or from the specified
\var{offset
}). The slice will extend to the
89 end of
\var{object
} (or will have a length given by the
\var{size
}
93 \begin{funcdesc
}{callable
}{object
}
94 Return true if the
\var{object
} argument appears callable, false if
95 not. If this returns true, it is still possible that a call fails,
96 but if it is false, calling
\var{object
} will never succeed. Note
97 that classes are callable (calling a class returns a new instance);
98 class instances are callable if they have a
\method{__call__()
} method.
101 \begin{funcdesc
}{chr
}{i
}
102 Return a string of one character whose
\ASCII{} code is the integer
103 \var{i
}, e.g.,
\code{chr(
97)
} returns the string
\code{'a'
}. This is the
104 inverse of
\function{ord()
}. The argument must be in the range
[0.
.255],
108 \begin{funcdesc
}{cmp
}{x, y
}
109 Compare the two objects
\var{x
} and
\var{y
} and return an integer
110 according to the outcome. The return value is negative if
\code{\var{x
}
111 <
\var{y
}}, zero if
\code{\var{x
} ==
\var{y
}} and strictly positive if
112 \code{\var{x
} >
\var{y
}}.
115 \begin{funcdesc
}{coerce
}{x, y
}
116 Return a tuple consisting of the two numeric arguments converted to
117 a common type, using the same rules as used by arithmetic
121 \begin{funcdesc
}{compile
}{string, filename, kind
}
122 Compile the
\var{string
} into a code object. Code objects can be
123 executed by an
\keyword{exec
} statement or evaluated by a call to
124 \function{eval()
}. The
\var{filename
} argument should
125 give the file from which the code was read; pass e.g.
\code{'<string>'
}
126 if it wasn't read from a file. The
\var{kind
} argument specifies
127 what kind of code must be compiled; it can be
\code{'exec'
} if
128 \var{string
} consists of a sequence of statements,
\code{'eval'
}
129 if it consists of a single expression, or
\code{'single'
} if
130 it consists of a single interactive statement (in the latter case,
131 expression statements that evaluate to something else than
132 \code{None
} will printed).
135 \begin{funcdesc
}{complex
}{real
\optional{, imag
}}
136 Create a complex number with the value
\var{real
} +
\var{imag
}*j or
137 convert a string or number to a complex number.
138 Each argument may be any numeric type (including complex).
139 If
\var{imag
} is omitted, it defaults to zero and the function
140 serves as a numeric conversion function like
\function{int()
},
141 \function{long()
} and
\function{float()
}; in this case it also
142 accepts a string argument which should be a valid complex number.
145 \begin{funcdesc
}{delattr
}{object, name
}
146 This is a relative of
\function{setattr()
}. The arguments are an
147 object and a string. The string must be the name
148 of one of the object's attributes. The function deletes
149 the named attribute, provided the object allows it. For example,
150 \code{delattr(
\var{x
}, '
\var{foobar
}')
} is equivalent to
151 \code{del
\var{x
}.
\var{foobar
}}.
154 \begin{funcdesc
}{dir
}{\optional{object
}}
155 Without arguments, return the list of names in the current local
156 symbol table. With an argument, attempts to return a list of valid
157 attribute for that object. This information is gleaned from the
158 object's
\member{__dict__
},
\member{__methods__
} and
\member{__members__
}
159 attributes, if defined. The list is not necessarily complete; e.g.,
160 for classes, attributes defined in base classes are not included,
161 and for class instances, methods are not included.
162 The resulting list is sorted alphabetically. For example:
169 ['argv', 'exit', 'modules', 'path', 'stderr', 'stdin', 'stdout'
]
174 \begin{funcdesc
}{divmod
}{a, b
}
175 Take two numbers as arguments and return a pair of numbers consisting
176 of their quotient and remainder when using long division. With mixed
177 operand types, the rules for binary arithmetic operators apply. For
178 plain and long integers, the result is the same as
179 \code{(
\var{a
} /
\var{b
},
\var{a
} \%
{} \var{b
})
}.
180 For floating point numbers the result is
\code{(
\var{q
},
\var{a
} \%
{}
181 \var{b
})
}, where
\var{q
} is usually
\code{math.floor(
\var{a
} /
182 \var{b
})
} but may be
1 less than that. In any case
\code{\var{q
} *
183 \var{b
} +
\var{a
} \%
{} \var{b
}} is very close to
\var{a
}, if
184 \code{\var{a
} \%
{} \var{b
}} is non-zero it has the same sign as
185 \var{b
}, and
\code{0 <= abs(
\var{a
} \%
{} \var{b
}) < abs(
\var{b
})
}.
188 \begin{funcdesc
}{eval
}{expression
\optional{, globals
\optional{, locals
}}}
189 The arguments are a string and two optional dictionaries. The
190 \var{expression
} argument is parsed and evaluated as a Python
191 expression (technically speaking, a condition list) using the
192 \var{globals
} and
\var{locals
} dictionaries as global and local name
193 space. If the
\var{locals
} dictionary is omitted it defaults to
194 the
\var{globals
} dictionary. If both dictionaries are omitted, the
195 expression is executed in the environment where
\keyword{eval
} is
196 called. The return value is the result of the evaluated expression.
197 Syntax errors are reported as exceptions. Example:
201 >>> print eval('x+
1')
205 This function can also be used to execute arbitrary code objects
206 (e.g.\ created by
\function{compile()
}). In this case pass a code
207 object instead of a string. The code object must have been compiled
208 passing
\code{'eval'
} to the
\var{kind
} argument.
210 Hints: dynamic execution of statements is supported by the
211 \keyword{exec
} statement. Execution of statements from a file is
212 supported by the
\function{execfile()
} function. The
213 \function{globals()
} and
\function{locals()
} functions returns the
214 current global and local dictionary, respectively, which may be
215 useful to pass around for use by
\function{eval()
} or
216 \function{execfile()
}.
219 \begin{funcdesc
}{execfile
}{file
\optional{, globals
\optional{, locals
}}}
220 This function is similar to the
221 \keyword{exec
} statement, but parses a file instead of a string. It
222 is different from the
\keyword{import
} statement in that it does not
223 use the module administration --- it reads the file unconditionally
224 and does not create a new module.
\footnote{It is used relatively
225 rarely so does not warrant being made into a statement.
}
227 The arguments are a file name and two optional dictionaries. The
228 file is parsed and evaluated as a sequence of Python statements
229 (similarly to a module) using the
\var{globals
} and
\var{locals
}
230 dictionaries as global and local name space. If the
\var{locals
}
231 dictionary is omitted it defaults to the
\var{globals
} dictionary.
232 If both dictionaries are omitted, the expression is executed in the
233 environment where
\function{execfile()
} is called. The return value is
237 \begin{funcdesc
}{filter
}{function, list
}
238 Construct a list from those elements of
\var{list
} for which
239 \var{function
} returns true. If
\var{list
} is a string or a tuple,
240 the result also has that type; otherwise it is always a list. If
241 \var{function
} is
\code{None
}, the identity function is assumed,
242 i.e.\ all elements of
\var{list
} that are false (zero or empty) are
246 \begin{funcdesc
}{float
}{x
}
247 Convert a string or a number to floating point. If the argument is a
248 string, it must contain a possibly signed decimal or floating point
249 number, possibly embedded in whitespace; this behaves identical to
250 \code{string.atof(
\var{x
})
}. Otherwise, the argument may be a plain
251 or long integer or a floating point number, and a floating point
252 number with the same value (within Python's floating point
253 precision) is returned.
255 \strong{Note:
} When passing in a string, values for NaN
\index{NaN
}
256 and Infinity
\index{Infinity
} may be returned, depending on the
257 underlying C library. The specific set of strings accepted which
258 cause these values to be returned depends entirely on the C library
259 and is known to vary.
262 \begin{funcdesc
}{getattr
}{object, name
\optional{, default
}}
263 Return the value of the named attributed of
\var{object
}.
\var{name
}
264 must be a string. If the string is the name of one of the object's
265 attributes, the result is the value of that attribute. For example,
266 \code{getattr(x, 'foobar')
} is equivalent to
\code{x.foobar
}. If the
267 named attribute does not exist,
\var{default
} is returned if provided,
268 otherwise
\exception{AttributeError
} is raised.
271 \begin{funcdesc
}{globals
}{}
272 Return a dictionary representing the current global symbol table.
273 This is always the dictionary of the current module (inside a
274 function or method, this is the module where it is defined, not the
275 module from which it is called).
278 \begin{funcdesc
}{hasattr
}{object, name
}
279 The arguments are an object and a string. The result is
1 if the
280 string is the name of one of the object's attributes,
0 if not.
281 (This is implemented by calling
\code{getattr(
\var{object
},
282 \var{name
})
} and seeing whether it raises an exception or not.)
285 \begin{funcdesc
}{hash
}{object
}
286 Return the hash value of the object (if it has one). Hash values
287 are integers. They are used to quickly compare dictionary
288 keys during a dictionary lookup. Numeric values that compare equal
289 have the same hash value (even if they are of different types, e.g.
293 \begin{funcdesc
}{hex
}{x
}
294 Convert an integer number (of any size) to a hexadecimal string.
295 The result is a valid Python expression. Note: this always yields
296 an unsigned literal, e.g. on a
32-bit machine,
\code{hex(-
1)
} yields
297 \code{'
0xffffffff'
}. When evaluated on a machine with the same
298 word size, this literal is evaluated as -
1; at a different word
299 size, it may turn up as a large positive number or raise an
300 \exception{OverflowError
} exception.
303 \begin{funcdesc
}{id
}{object
}
304 Return the `identity' of an object. This is an integer which is
305 guaranteed to be unique and constant for this object during its
306 lifetime. (Two objects whose lifetimes are disjunct may have the
307 same
\function{id()
} value.) (Implementation note: this is the
308 address of the object.)
311 \begin{funcdesc
}{input
}{\optional{prompt
}}
312 Equivalent to
\code{eval(raw_input(
\var{prompt
}))
}.
315 \begin{funcdesc
}{intern
}{string
}
316 Enter
\var{string
} in the table of ``interned'' strings and return
317 the interned string -- which is
\var{string
} itself or a copy.
318 Interning strings is useful to gain a little performance on
319 dictionary lookup -- if the keys in a dictionary are interned, and
320 the lookup key is interned, the key comparisons (after hashing) can
321 be done by a pointer compare instead of a string compare. Normally,
322 the names used in Python programs are automatically interned, and
323 the dictionaries used to hold module, class or instance attributes
324 have interned keys. Interned strings are immortal (i.e. never get
328 \begin{funcdesc
}{int
}{x
}
329 Convert a string or number to a plain integer. If the argument is a
330 string, it must contain a possibly signed decimal number
331 representable as a Python integer, possibly embedded in whitespace;
332 this behaves identical to
\code{string.atoi(
\var{x
})
}.
333 Otherwise, the argument may be a plain or
334 long integer or a floating point number. Conversion of floating
335 point numbers to integers is defined by the C semantics; normally
336 the conversion truncates towards zero.
\footnote{This is ugly --- the
337 language definition should require truncation towards zero.
}
340 \begin{funcdesc
}{isinstance
}{object, class
}
341 Return true if the
\var{object
} argument is an instance of the
342 \var{class
} argument, or of a (direct or indirect) subclass thereof.
343 Also return true if
\var{class
} is a type object and
\var{object
} is
344 an object of that type. If
\var{object
} is not a class instance or a
345 object of the given type, the function always returns false. If
346 \var{class
} is neither a class object nor a type object, a
347 \exception{TypeError
} exception is raised.
350 \begin{funcdesc
}{issubclass
}{class1, class2
}
351 Return true if
\var{class1
} is a subclass (direct or indirect) of
352 \var{class2
}. A class is considered a subclass of itself. If either
353 argument is not a class object, a
\exception{TypeError
} exception is
357 \begin{funcdesc
}{len
}{s
}
358 Return the length (the number of items) of an object. The argument
359 may be a sequence (string, tuple or list) or a mapping (dictionary).
362 \begin{funcdesc
}{list
}{sequence
}
363 Return a list whose items are the same and in the same order as
364 \var{sequence
}'s items. If
\var{sequence
} is already a list,
365 a copy is made and returned, similar to
\code{\var{sequence
}[:
]}.
366 For instance,
\code{list('abc')
} returns
367 returns
\code{['a', 'b', 'c'
]} and
\code{list( (
1,
2,
3) )
} returns
371 \begin{funcdesc
}{locals
}{}
372 Return a dictionary representing the current local symbol table.
373 \strong{Warning:
} the contents of this dictionary should not be
374 modified; changes may not affect the values of local variables used by
378 \begin{funcdesc
}{long
}{x
}
379 Convert a string or number to a long integer. If the argument is a
380 string, it must contain a possibly signed decimal number of
381 arbitrary size, possibly embedded in whitespace;
382 this behaves identical to
\code{string.atol(
\var{x
})
}.
383 Otherwise, the argument may be a plain or
384 long integer or a floating point number, and a long integer with
385 the same value is returned. Conversion of floating
386 point numbers to integers is defined by the C semantics;
387 see the description of
\function{int()
}.
390 \begin{funcdesc
}{map
}{function, list, ...
}
391 Apply
\var{function
} to every item of
\var{list
} and return a list
392 of the results. If additional
\var{list
} arguments are passed,
393 \var{function
} must take that many arguments and is applied to
394 the items of all lists in parallel; if a list is shorter than another
395 it is assumed to be extended with
\code{None
} items. If
396 \var{function
} is
\code{None
}, the identity function is assumed; if
397 there are multiple list arguments,
\function{map()
} returns a list
398 consisting of tuples containing the corresponding items from all lists
399 (i.e. a kind of transpose operation). The
\var{list
} arguments may be
400 any kind of sequence; the result is always a list.
403 \begin{funcdesc
}{max
}{s
\optional{, args...
}}
404 With a single argument
\var{s
}, return the largest item of a
405 non-empty sequence (e.g., a string, tuple or list). With more than
406 one argument, return the largest of the arguments.
409 \begin{funcdesc
}{min
}{s
\optional{, args...
}}
410 With a single argument
\var{s
}, return the smallest item of a
411 non-empty sequence (e.g., a string, tuple or list). With more than
412 one argument, return the smallest of the arguments.
415 \begin{funcdesc
}{oct
}{x
}
416 Convert an integer number (of any size) to an octal string. The
417 result is a valid Python expression. Note: this always yields
418 an unsigned literal, e.g. on a
32-bit machine,
\code{oct(-
1)
} yields
419 \code{'
037777777777'
}. When evaluated on a machine with the same
420 word size, this literal is evaluated as -
1; at a different word
421 size, it may turn up as a large positive number or raise an
422 \exception{OverflowError
} exception.
425 \begin{funcdesc
}{open
}{filename
\optional{, mode
\optional{, bufsize
}}}
426 Return a new file object (described earlier under Built-in Types).
427 The first two arguments are the same as for
\code{stdio
}'s
428 \cfunction{fopen()
}:
\var{filename
} is the file name to be opened,
429 \var{mode
} indicates how the file is to be opened:
\code{'r'
} for
430 reading,
\code{'w'
} for writing (truncating an existing file), and
431 \code{'a'
} opens it for appending (which on
\emph{some
} \UNIX{}
432 systems means that
\emph{all
} writes append to the end of the file,
433 regardless of the current seek position).
435 Modes
\code{'r+'
},
\code{'w+'
} and
\code{'a+'
} open the file for
436 updating (note that
\code{'w+'
} truncates the file). Append
437 \code{'b'
} to the mode to open the file in binary mode, on systems
438 that differentiate between binary and text files (else it is
439 ignored). If the file cannot be opened,
\exception{IOError
} is
442 If
\var{mode
} is omitted, it defaults to
\code{'r'
}. When opening a
443 binary file, you should append
\code{'b'
} to the
\var{mode
} value
444 for improved portability. (It's useful even on systems which don't
445 treat binary and text files differently, where it serves as
447 \index{line-buffered I/O
}\index{unbuffered I/O
}\index{buffer size, I/O
}
448 \index{I/O control!buffering
}
449 The optional
\var{bufsize
} argument specifies the
450 file's desired buffer size:
0 means unbuffered,
1 means line
451 buffered, any other positive value means use a buffer of
452 (approximately) that size. A negative
\var{bufsize
} means to use
453 the system default, which is usually line buffered for for tty
454 devices and fully buffered for other files. If omitted, the system
455 default is used.
\footnote{
456 Specifying a buffer size currently has no effect on systems that
457 don't have
\cfunction{setvbuf()
}. The interface to specify the
458 buffer size is not done using a method that calls
459 \cfunction{setvbuf()
}, because that may dump core when called
460 after any I/O has been performed, and there's no reliable way to
461 determine whether this is the case.
}
464 \begin{funcdesc
}{ord
}{c
}
465 Return the
\ASCII{} value of a string of one character. E.g.,
466 \code{ord('a')
} returns the integer
\code{97}. This is the inverse of
470 \begin{funcdesc
}{pow
}{x, y
\optional{, z
}}
471 Return
\var{x
} to the power
\var{y
}; if
\var{z
} is present, return
472 \var{x
} to the power
\var{y
}, modulo
\var{z
} (computed more
473 efficiently than
\code{pow(
\var{x
},
\var{y
}) \%\
\var{z
}}).
474 The arguments must have
475 numeric types. With mixed operand types, the rules for binary
476 arithmetic operators apply. The effective operand type is also the
477 type of the result; if the result is not expressible in this type, the
478 function raises an exception; e.g.,
\code{pow(
2, -
1)
} or
\code{pow(
2,
479 35000)
} is not allowed.
482 \begin{funcdesc
}{range
}{\optional{start,
} stop
\optional{, step
}}
483 This is a versatile function to create lists containing arithmetic
484 progressions. It is most often used in
\keyword{for
} loops. The
485 arguments must be plain integers. If the
\var{step
} argument is
486 omitted, it defaults to
\code{1}. If the
\var{start
} argument is
487 omitted, it defaults to
\code{0}. The full form returns a list of
488 plain integers
\code{[\var{start
},
\var{start
} +
\var{step
},
489 \var{start
} +
2 *
\var{step
},
\ldots]}. If
\var{step
} is positive,
490 the last element is the largest
\code{\var{start
} +
\var{i
} *
491 \var{step
}} less than
\var{stop
}; if
\var{step
} is negative, the last
492 element is the largest
\code{\var{start
} +
\var{i
} *
\var{step
}}
493 greater than
\var{stop
}.
\var{step
} must not be zero (or else
494 \exception{ValueError
} is raised). Example:
498 [0,
1,
2,
3,
4,
5,
6,
7,
8,
9]
500 [1,
2,
3,
4,
5,
6,
7,
8,
9,
10]
502 [0,
5,
10,
15,
20,
25]
505 >>> range(
0, -
10, -
1)
506 [0, -
1, -
2, -
3, -
4, -
5, -
6, -
7, -
8, -
9]
515 \begin{funcdesc
}{raw_input
}{\optional{prompt
}}
516 If the
\var{prompt
} argument is present, it is written to standard output
517 without a trailing newline. The function then reads a line from input,
518 converts it to a string (stripping a trailing newline), and returns that.
519 When
\EOF{} is read,
\exception{EOFError
} is raised. Example:
522 >>> s = raw_input('--> ')
523 --> Monty Python's Flying Circus
525 "Monty Python's Flying Circus"
529 If the
\module{readline
} module was loaded, then
530 \function{raw_input()
} will use it to provide elaborate
531 line editing and history features.
534 \begin{funcdesc
}{reduce
}{function, sequence
\optional{, initializer
}}
535 Apply
\var{function
} of two arguments cumulatively to the items of
536 \var{sequence
}, from left to right, so as to reduce the sequence to
537 a single value. For example,
538 \code{reduce(lambda x, y: x+y,
[1,
2,
3,
4,
5])
} calculates
539 \code{((((
1+
2)+
3)+
4)+
5)
}.
540 If the optional
\var{initializer
} is present, it is placed before the
541 items of the sequence in the calculation, and serves as a default when
542 the sequence is empty.
545 \begin{funcdesc
}{reload
}{module
}
546 Re-parse and re-initialize an already imported
\var{module
}. The
547 argument must be a module object, so it must have been successfully
548 imported before. This is useful if you have edited the module source
549 file using an external editor and want to try out the new version
550 without leaving the Python interpreter. The return value is the
551 module object (i.e.\ the same as the
\var{module
} argument).
553 There are a number of caveats:
555 If a module is syntactically correct but its initialization fails, the
556 first
\keyword{import
} statement for it does not bind its name locally,
557 but does store a (partially initialized) module object in
558 \code{sys.modules
}. To reload the module you must first
559 \keyword{import
} it again (this will bind the name to the partially
560 initialized module object) before you can
\function{reload()
} it.
562 When a module is reloaded, its dictionary (containing the module's
563 global variables) is retained. Redefinitions of names will override
564 the old definitions, so this is generally not a problem. If the new
565 version of a module does not define a name that was defined by the old
566 version, the old definition remains. This feature can be used to the
567 module's advantage if it maintains a global table or cache of objects
568 --- with a
\keyword{try
} statement it can test for the table's presence
569 and skip its initialization if desired.
571 It is legal though generally not very useful to reload built-in or
572 dynamically loaded modules, except for
\module{sys
},
\module{__main__
}
573 and
\module{__builtin__
}. In certain cases, however, extension
574 modules are not designed to be initialized more than once, and may
575 fail in arbitrary ways when reloaded.
577 If a module imports objects from another module using
\keyword{from
}
578 \ldots{} \keyword{import
} \ldots{}, calling
\function{reload()
} for
579 the other module does not redefine the objects imported from it ---
580 one way around this is to re-execute the
\keyword{from
} statement,
581 another is to use
\keyword{import
} and qualified names
582 (
\var{module
}.
\var{name
}) instead.
584 If a module instantiates instances of a class, reloading the module
585 that defines the class does not affect the method definitions of the
586 instances --- they continue to use the old class definition. The same
587 is true for derived classes.
590 \begin{funcdesc
}{repr
}{object
}
591 Return a string containing a printable representation of an object.
592 This is the same value yielded by conversions (reverse quotes).
593 It is sometimes useful to be able to access this operation as an
594 ordinary function. For many types, this function makes an attempt
595 to return a string that would yield an object with the same value
596 when passed to
\function{eval()
}.
599 \begin{funcdesc
}{round
}{x
\optional{, n
}}
600 Return the floating point value
\var{x
} rounded to
\var{n
} digits
601 after the decimal point. If
\var{n
} is omitted, it defaults to zero.
602 The result is a floating point number. Values are rounded to the
603 closest multiple of
10 to the power minus
\var{n
}; if two multiples
604 are equally close, rounding is done away from
0 (so e.g.
605 \code{round(
0.5)
} is
\code{1.0} and
\code{round(-
0.5)
} is
\code{-
1.0}).
608 \begin{funcdesc
}{setattr
}{object, name, value
}
609 This is the counterpart of
\function{getattr()
}. The arguments are an
610 object, a string and an arbitrary value. The string may name an
611 existing attribute or a new attribute. The function assigns the
612 value to the attribute, provided the object allows it. For example,
613 \code{setattr(
\var{x
}, '
\var{foobar
}',
123)
} is equivalent to
614 \code{\var{x
}.
\var{foobar
} =
123}.
617 \begin{funcdesc
}{slice
}{\optional{start,
} stop
\optional{, step
}}
618 Return a slice object representing the set of indices specified by
619 \code{range(
\var{start
},
\var{stop
},
\var{step
})
}. The
\var{start
}
620 and
\var{step
} arguments default to None. Slice objects have
621 read-only data attributes
\member{start
},
\member{stop
} and
\member{step
}
622 which merely return the argument values (or their default). They have
623 no other explicit functionality; however they are used by Numerical
624 Python
\index{Numerical Python
} and other third party extensions.
625 Slice objects are also generated when extended indexing syntax is
626 used, e.g. for
\samp{a
[start:stop:step
]} or
\samp{a
[start:stop, i
]}.
629 \begin{funcdesc
}{str
}{object
}
630 Return a string containing a nicely printable representation of an
631 object. For strings, this returns the string itself. The difference
632 with
\code{repr(
\var{object
})
} is that
\code{str(
\var{object
})
} does not
633 always attempt to return a string that is acceptable to
\function{eval()
};
634 its goal is to return a printable string.
637 \begin{funcdesc
}{tuple
}{sequence
}
638 Return a tuple whose items are the same and in the same order as
639 \var{sequence
}'s items. If
\var{sequence
} is already a tuple, it
640 is returned unchanged. For instance,
\code{tuple('abc')
} returns
641 returns
\code{('a', 'b', 'c')
} and
\code{tuple(
[1,
2,
3])
} returns
645 \begin{funcdesc
}{type
}{object
}
646 Return the type of an
\var{object
}. The return value is a type
647 object. The standard module
\module{types
} defines names for all
649 \refstmodindex{types
}
655 >>> if type(x) == types.StringType: print "It's a string"
659 \begin{funcdesc
}{vars
}{\optional{object
}}
660 Without arguments, return a dictionary corresponding to the current
661 local symbol table. With a module, class or class instance object as
662 argument (or anything else that has a
\member{__dict__
} attribute),
663 returns a dictionary corresponding to the object's symbol table.
664 The returned dictionary should not be modified: the effects on the
665 corresponding symbol table are undefined.
\footnote{
666 In the current implementation, local variable bindings cannot
667 normally be affected this way, but variables retrieved from
668 other scopes (e.g. modules) can be. This may change.
}
671 \begin{funcdesc
}{xrange
}{\optional{start,
} stop
\optional{, step
}}
672 This function is very similar to
\function{range()
}, but returns an
673 ``xrange object'' instead of a list. This is an opaque sequence type
674 which yields the same values as the corresponding list, without
675 actually storing them all simultaneously. The advantage of
676 \function{xrange()
} over
\function{range()
} is minimal (since
677 \function{xrange()
} still has to create the values when asked for
678 them) except when a very large range is used on a memory-starved
679 machine (e.g. MS-DOS) or when all of the range's elements are never
680 used (e.g. when the loop is usually terminated with
\keyword{break
}).
