2. 内置函数¶

The Python interpreter has a number of functions built into it that are always available. They are listed here in alphabetical order.

		内置函数
`abs()`	`divmod()`	`input()`	`open()`	`staticmethod()`
`all()`	`enumerate()`	`int()`	`ord()`	`str()`
`any()`	`eval()`	`isinstance()`	`pow()`	`sum()`
`basestring()`	`execfile()`	`issubclass()`	`print()`	`super()`
`bin()`	`file()`	`iter()`	`property()`	`tuple()`
`bool()`	`filter()`	`len()`	`range()`	`type()`
`bytearray()`	`float()`	`list()`	`raw_input()`	`unichr()`
`callable()`	`format()`	`locals()`	`reduce()`	`unicode()`
`chr()`	`frozenset()`	`long()`	`reload()`	`vars()`
`classmethod()`	`getattr()`	`map()`	`repr()`	`xrange()`
`cmp()`	`globals()`	`max()`	`reversed()`	`zip()`
`compile()`	`hasattr()`	`memoryview()`	`round()`	`__import__()`
`complex()`	`hash()`	`min()`	`set()`
`delattr()`	`help()`	`next()`	`setattr()`
`dict()`	`hex()`	`object()`	`slice()`
`dir()`	`id()`	`oct()`	`sorted()`

In addition, there are other four built-in functions that are no longer considered essential: apply(), buffer(), coerce(), and intern(). They are documented in the Non-essential Built-in Functions section.

abs(x)¶: Return the absolute value of a number. The argument may be a plain or long integer or a floating point number. If the argument is a complex number, its magnitude is returned.

all(iterable)¶

如果 iterable 的所有元素为真（或迭代器为空），返回 True 。等价于:

def all(iterable):
    for element in iterable:
        if not element:
            return False
    return True

2.5 新版功能.

any(iterable)¶

如果*iterable*的任一元素为真则返回``True``。如果迭代器为空，返回``False``。等价于:

def any(iterable):
    for element in iterable:
        if element:
            return True
    return False

2.5 新版功能.

basestring()¶: This abstract type is the superclass for str and unicode. It cannot be called or instantiated, but it can be used to test whether an object is an instance of str or unicode. isinstance(obj, basestring) is equivalent to isinstance(obj, (str, unicode)).

2.3 新版功能.

bin(x)¶: Convert an integer number to a binary string. The result is a valid Python expression. If x is not a Python int object, it has to define an __index__() method that returns an integer.

2.6 新版功能.

class bool([x])¶: Return a Boolean value, i.e. one of True or False. x is converted using the standard truth testing procedure. If x is false or omitted, this returns False; otherwise it returns True. bool is also a class, which is a subclass of int. Class bool cannot be subclassed further. Its only instances are False and True.

2.2.1 新版功能.

在 2.3 版更改: If no argument is given, this function returns False.

class bytearray([source[, encoding[, errors]]])¶

Return a new array of bytes. The bytearray class is a mutable sequence of integers in the range 0 <= x < 256. It has most of the usual methods of mutable sequences, described in 可变序列类型, as well as most methods that the str type has, see 字符串的方法.

可选形参 source 可以用不同的方式来初始化数组：

If it is unicode, you must also give the encoding (and optionally, errors) parameters; bytearray() then converts the unicode to bytes using unicode.encode().
如果是一个 integer，会初始化大小为该数字的数组，并使用 null 字节填充。
如果是一个符合 buffer 接口的对象，该对象的只读 buffer 会用来初始化字节数组。
如果是一个 iterable 可迭代对象，它的元素的范围必须是 0 <= x < 256 的整数，它会被用作数组的初始内容。

如果没有实参，则创建大小为 0 的数组。

2.6 新版功能.

callable(object)¶: Return True if the object argument appears callable, False if not. If this returns true, it is still possible that a call fails, but if it is false, calling object will never succeed. Note that classes are callable (calling a class returns a new instance); class instances are callable if they have a __call__() method.

chr(i)¶: Return a string of one character whose ASCII code is the integer i. For example, chr(97) returns the string 'a'. This is the inverse of ord(). The argument must be in the range [0..255], inclusive; ValueError will be raised if i is outside that range. See also unichr().

classmethod(function)¶

Return a class method for function.

一个类方法把类自己作为第一个实参，就像一个实例方法把实例自己作为第一个实参。请用以下习惯来声明类方法:

class C(object):
    @classmethod
    def f(cls, arg1, arg2, ...):
        ...

@classmethod 这样的形式称为函数的 decorator – 详情参阅函数定义。

类方法的调用可以在类上进行 (例如 C.f()) 也可以在实际上进行 (例如 C().f())。其所属类以外的类实例会被忽略。如果类方法在其所属类的派生类上调用，则该派生类对象会被作为隐含的第一个参数被传入。

类方法与 C++ 或 Java 中的静态方法不同。如果你需要后者，请参阅 staticmethod()。

想了解更多有关类方法的信息，请参阅标准类型层级结构。

2.2 新版功能.

在 2.4 版更改: Function decorator syntax added.

cmp(x, y)¶: Compare the two objects x and y and return an integer according to the outcome. The return value is negative if x < y, zero if x == y and strictly positive if x > y.

compile(source, filename, mode[, flags[, dont_inherit]])¶

Compile the source into a code or AST object. Code objects can be executed by an exec statement or evaluated by a call to eval(). source can either be a Unicode string, a Latin-1 encoded string or an AST object. Refer to the ast module documentation for information on how to work with AST objects.

filename 实参需要是代码读取的文件名；如果代码不需要从文件中读取，可以传入一些可辨识的值（经常会使用 '<string>'）。

mode 实参指定了编译代码必须用的模式。如果 source 是语句序列，可以是 'exec'；如果是单一表达式，可以是 'eval'；如果是单个交互式语句，可以是 'single'。（在最后一种情况下，如果表达式执行结果不是 None 将会被打印出来。）

The optional arguments flags and dont_inherit control which future statements (see PEP 236) affect the compilation of source. If neither is present (or both are zero) the code is compiled with those future statements that are in effect in the code that is calling compile(). If the flags argument is given and dont_inherit is not (or is zero) then the future statements specified by the flags argument are used in addition to those that would be used anyway. If dont_inherit is a non-zero integer then the flags argument is it – the future statements in effect around the call to compile are ignored.

Future 语句使用比特位来指定，多个语句可以通过按位或来指定。具体特性的比特位可以通过 __future__ 模块中的 _Feature 类的实例的 compiler_flag 属性来获得。

This function raises SyntaxError if the compiled source is invalid, and TypeError if the source contains null bytes.

如果您想分析 Python 代码的 AST 表示，请参阅 ast.parse()。

注解

在 'single' 或 'eval' 模式编译多行代码字符串时，输入必须以至少一个换行符结尾。这使 code 模块更容易检测语句的完整性。

在 2.3 版更改: The flags and dont_inherit arguments were added.

在 2.6 版更改: Support for compiling AST objects.

在 2.7 版更改: Allowed use of Windows and Mac newlines. Also input in 'exec' mode does not have to end in a newline anymore.

class complex([real[, imag]])¶

Return a complex number with the value real + imag*1j or convert a string or number to a complex number. If the first parameter is a string, it will be interpreted as a complex number and the function must be called without a second parameter. The second parameter can never be a string. Each argument may be any numeric type (including complex). If imag is omitted, it defaults to zero and the function serves as a numeric conversion function like int(), long() and float(). If both arguments are omitted, returns 0j.

注解

当从字符串转换时，字符串在 + 或 - 的周围必须不能有空格。例如 complex('1+2j') 是合法的，但 complex('1 + 2j') 会触发 ValueError 异常。

Numeric Types — int, float, long, complex 描述了复数类型。

delattr(object, name)¶: setattr() 相关的函数。实参是一个对象和一个字符串。该字符串必须是对象的某个属性。如果对象允许，该函数将删除指定的属性。例如 delattr(x, 'foobar') 等价于 del x.foobar 。

class dict(**kwarg)

class dict(mapping, **kwarg)

class dict(iterable, **kwarg)

创建一个新的字典。dict 对象是一个字典类。参见 dict 和映射类型 — dict 了解这个类。

其他容器类型，请参见内置的 list、set 和 tuple 类，以及 collections 模块。

dir([object])¶

如果没有实参，则返回当前本地作用域中的名称列表。如果有实参，它会尝试返回该对象的有效属性列表。

如果对象有一个名为 __dir__() 的方法，那么该方法将被调用，并且必须返回一个属性列表。这允许实现自定义 __getattr__() 或 __getattribute__() 函数的对象能够自定义 dir() 来报告它们的属性。

如果对象不提供 __dir__()，这个函数会尝试从对象已定义的 __dict__ 属性和类型对象收集信息。结果列表并不总是完整的，如果对象有自定义 __getattr__()，那结果可能不准确。

默认的 dir() 机制对不同类型的对象行为不同，它会试图返回最相关而不是最全的信息：

如果对象是模块对象，则列表包含模块的属性名称。
如果对象是类型或类对象，则列表包含它们的属性名称，并且递归查找所有基类的属性。
否则，列表包含对象的属性名称，它的类属性名称，并且递归查找它的类的所有基类的属性。

返回的列表按字母表排序。例如：

>>> import struct
>>> dir()   # show the names in the module namespace
['__builtins__', '__doc__', '__name__', 'struct']
>>> dir(struct)   # show the names in the struct module
['Struct', '__builtins__', '__doc__', '__file__', '__name__',
 '__package__', '_clearcache', 'calcsize', 'error', 'pack', 'pack_into',
 'unpack', 'unpack_from']
>>> class Shape(object):
        def __dir__(self):
            return ['area', 'perimeter', 'location']
>>> s = Shape()
>>> dir(s)
['area', 'perimeter', 'location']

注解

因为 dir() 主要是为了便于在交互式时使用，所以它会试图返回人们感兴趣的名字集合，而不是试图保证结果的严格性或一致性，它具体的行为也可能在不同版本之间改变。例如，当实参是一个类时，metaclass 的属性不包含在结果列表中。

divmod(a, b)¶: Take two (non complex) numbers as arguments and return a pair of numbers consisting of their quotient and remainder when using long division. With mixed operand types, the rules for binary arithmetic operators apply. For plain and long integers, the result is the same as (a // b, a % b). For floating point numbers the result is (q, a % b), where q is usually math.floor(a / b) but may be 1 less than that. In any case q * b + a % b is very close to a, if a % b is non-zero it has the same sign as b, and 0 <= abs(a % b) < abs(b).

在 2.3 版更改: Using divmod() with complex numbers is deprecated.

enumerate(sequence, start=0)¶

Return an enumerate object. sequence must be a sequence, an iterator, or some other object which supports iteration. The next() method of the iterator returned by enumerate() returns a tuple containing a count (from start which defaults to 0) and the values obtained from iterating over sequence:

>>> seasons = ['Spring', 'Summer', 'Fall', 'Winter']
>>> list(enumerate(seasons))
[(0, 'Spring'), (1, 'Summer'), (2, 'Fall'), (3, 'Winter')]
>>> list(enumerate(seasons, start=1))
[(1, 'Spring'), (2, 'Summer'), (3, 'Fall'), (4, 'Winter')]

等价于:

def enumerate(sequence, start=0):
    n = start
    for elem in sequence:
        yield n, elem
        n += 1

2.3 新版功能.

在 2.6 版更改: The start parameter was added.

eval(expression[, globals[, locals]])¶

The arguments are a Unicode or Latin-1 encoded string and optional globals and locals. If provided, globals must be a dictionary. If provided, locals can be any mapping object.

在 2.4 版更改: formerly locals was required to be a dictionary.

The expression argument is parsed and evaluated as a Python expression (technically speaking, a condition list) using the globals and locals dictionaries as global and local namespace. If the globals dictionary is present and lacks ‘__builtins__’, the current globals are copied into globals before expression is parsed. This means that expression normally has full access to the standard __builtin__ module and restricted environments are propagated. If the locals dictionary is omitted it defaults to the globals dictionary. If both dictionaries are omitted, the expression is executed in the environment where eval() is called. The return value is the result of the evaluated expression. Syntax errors are reported as exceptions. Example:

>>> x = 1
>>> print eval('x+1')
2

这个函数也可以用来执行任何代码对象（如 compile() 创建的）。这种情况下，参数是代码对象，而不是字符串。如果编译该对象时的 mode 实参是 'exec' 那么 eval() 返回值为 None 。

Hints: dynamic execution of statements is supported by the exec statement. Execution of statements from a file is supported by the execfile() function. The globals() and locals() functions returns the current global and local dictionary, respectively, which may be useful to pass around for use by eval() or execfile().

另外可以参阅 ast.literal_eval()，该函数可以安全执行仅包含文字的表达式字符串。

execfile(filename[, globals[, locals]])¶

This function is similar to the exec statement, but parses a file instead of a string. It is different from the import statement in that it does not use the module administration — it reads the file unconditionally and does not create a new module. [1]

The arguments are a file name and two optional dictionaries. The file is parsed and evaluated as a sequence of Python statements (similarly to a module) using the globals and locals dictionaries as global and local namespace. If provided, locals can be any mapping object. Remember that at module level, globals and locals are the same dictionary. If two separate objects are passed as globals and locals, the code will be executed as if it were embedded in a class definition.

在 2.4 版更改: formerly locals was required to be a dictionary.

If the locals dictionary is omitted it defaults to the globals dictionary. If both dictionaries are omitted, the expression is executed in the environment where execfile() is called. The return value is None.

注解

The default locals act as described for function locals() below: modifications to the default locals dictionary should not be attempted. Pass an explicit locals dictionary if you need to see effects of the code on locals after function execfile() returns. execfile() cannot be used reliably to modify a function’s locals.

file(name[, mode[, buffering]])¶

Constructor function for the file type, described further in section File Objects. The constructor’s arguments are the same as those of the open() built-in function described below.

When opening a file, it’s preferable to use open() instead of invoking this constructor directly. file is more suited to type testing (for example, writing isinstance(f, file)).

2.2 新版功能.

filter(function, iterable)¶

Construct a list from those elements of iterable for which function returns true. iterable may be either a sequence, a container which supports iteration, or an iterator. If iterable is a string or a tuple, the result also has that type; otherwise it is always a list. If function is None, the identity function is assumed, that is, all elements of iterable that are false are removed.

Note that filter(function, iterable) is equivalent to [item for item in iterable if function(item)] if function is not None and [item for item in iterable if item] if function is None.

See itertools.ifilter() and itertools.ifilterfalse() for iterator versions of this function, including a variation that filters for elements where the function returns false.

class float([x])¶

返回从数字或字符串 x 生成的浮点数。

If the argument is a string, it must contain a possibly signed decimal or floating point number, possibly embedded in whitespace. The argument may also be [+|-]nan or [+|-]inf. Otherwise, the argument may be a plain or long integer or a floating point number, and a floating point number with the same value (within Python’s floating point precision) is returned. If no argument is given, returns 0.0.

注解

When passing in a string, values for NaN and Infinity may be returned, depending on the underlying C library. Float accepts the strings nan, inf and -inf for NaN and positive or negative infinity. The case and a leading + are ignored as well as a leading - is ignored for NaN. Float always represents NaN and infinity as nan, inf or -inf.

Numeric Types — int, float, long, complex 描述了浮点类型。

format(value[, format_spec])¶: 将 value 转换为 format_spec 控制的“格式化”表示。format_spec 的解释取决于 value 实参的类型，但是大多数内置类型使用标准格式化语法：Format Specification Mini-Language。

注解

format(value, format_spec) merely calls value.__format__(format_spec).

2.6 新版功能.

class frozenset([iterable])

返回一个新的 frozenset 对象，它包含可选参数 iterable 中的元素。 frozenset 是一个内置的类。有关此类的文档，请参阅 frozenset 和集合类型 — set, frozenset。

请参阅内建的 set、list、tuple 和 dict 类，以及 collections 模块来了解其它的容器。

2.4 新版功能.

getattr(object, name[, default])¶: 返回对象命名属性的值。name 必须是字符串。如果该字符串是对象的属性之一，则返回该属性的值。例如， getattr(x, 'foobar') 等同于 x.foobar。如果指定的属性不存在，且提供了 default 值，则返回它，否则触发 AttributeError。

globals()¶: 返回表示当前全局符号表的字典。这总是当前模块的字典（在函数或方法中，不是调用它的模块，而是定义它的模块）。

hasattr(object, name)¶: The arguments are an object and a string. The result is True if the string is the name of one of the object’s attributes, False if not. (This is implemented by calling getattr(object, name) and seeing whether it raises an exception or not.)

hash(object)¶: Return the hash value of the object (if it has one). Hash values are integers. They are used to quickly compare dictionary keys during a dictionary lookup. Numeric values that compare equal have the same hash value (even if they are of different types, as is the case for 1 and 1.0).

help([object])¶

启动内置的帮助系统（此函数主要在交互式中使用）。如果没有实参，解释器控制台里会启动交互式帮助系统。如果实参是一个字符串，则在模块、函数、类、方法、关键字或文档主题中搜索该字符串，并在控制台上打印帮助信息。如果实参是其他任意对象，则会生成该对象的帮助页。

该函数通过 site 模块加入到内置命名空间。

2.2 新版功能.

hex(x)¶

Convert an integer number (of any size) to a lowercase hexadecimal string prefixed with “0x”, for example:

>>> hex(255)
'0xff'
>>> hex(-42)
'-0x2a'
>>> hex(1L)
'0x1L'

If x is not a Python int or long object, it has to define a __hex__() method that returns a string.

另请参阅 int() 将十六进制字符串转换为以 16 为基数的整数。

注解

如果要获取浮点数的十六进制字符串形式，请使用 float.hex() 方法。

在 2.4 版更改: Formerly only returned an unsigned literal.

id(object)¶: Return the “identity” of an object. This is an integer (or long integer) which is guaranteed to be unique and constant for this object during its lifetime. Two objects with non-overlapping lifetimes may have the same id() value.

CPython implementation detail: This is the address of the object in memory.

input([prompt])¶

Equivalent to eval(raw_input(prompt)).

This function does not catch user errors. If the input is not syntactically valid, a SyntaxError will be raised. Other exceptions may be raised if there is an error during evaluation.

如果加载了 readline 模块，input() 将使用它来提供复杂的行编辑和历史记录功能。

Consider using the raw_input() function for general input from users.

class int(x=0)¶

class int(x, base=10)

Return an integer object constructed from a number or string x, or return 0 if no arguments are given. If x is a number, it can be a plain integer, a long integer, or a floating point number. If x is floating point, the conversion truncates towards zero. If the argument is outside the integer range, the function returns a long object instead.

If x is not a number or if base is given, then x must be a string or Unicode object representing an integer literal in radix base. Optionally, the literal can be preceded by + or - (with no space in between) and surrounded by whitespace. A base-n literal consists of the digits 0 to n-1, with a to z (or A to Z) having values 10 to 35. The default base is 10. The allowed values are 0 and 2–36. Base-2, -8, and -16 literals can be optionally prefixed with 0b/0B, 0o/0O/0, or 0x/0X, as with integer literals in code. Base 0 means to interpret the string exactly as an integer literal, so that the actual base is 2, 8, 10, or 16.

整数类型定义请参阅 Numeric Types — int, float, long, complex 。

isinstance(object, classinfo)¶: Return true if the object argument is an instance of the classinfo argument, or of a (direct, indirect or virtual) subclass thereof. Also return true if classinfo is a type object (new-style class) and object is an object of that type or of a (direct, indirect or virtual) subclass thereof. If object is not a class instance or an object of the given type, the function always returns false. If classinfo is a tuple of class or type objects (or recursively, other such tuples), return true if object is an instance of any of the classes or types. If classinfo is not a class, type, or tuple of classes, types, and such tuples, a TypeError exception is raised.

在 2.2 版更改: Support for a tuple of type information was added.

issubclass(class, classinfo)¶: 如果 class 是 classinfo 的子类（直接、间接或虚拟的），则返回 true。classinfo 可以是类对象的元组，此时 classinfo 中的每个元素都会被检查。其他情况，会触发 TypeError 异常。

在 2.3 版更改: Support for a tuple of type information was added.

iter(o[, sentinel])¶

Return an iterator object. The first argument is interpreted very differently depending on the presence of the second argument. Without a second argument, o must be a collection object which supports the iteration protocol (the __iter__() method), or it must support the sequence protocol (the __getitem__() method with integer arguments starting at 0). If it does not support either of those protocols, TypeError is raised. If the second argument, sentinel, is given, then o must be a callable object. The iterator created in this case will call o with no arguments for each call to its next() method; if the value returned is equal to sentinel, StopIteration will be raised, otherwise the value will be returned.

One useful application of the second form of iter() is to read lines of a file until a certain line is reached. The following example reads a file until the readline() method returns an empty string:

with open('mydata.txt') as fp:
    for line in iter(fp.readline, ''):
        process_line(line)

2.2 新版功能.

len(s)¶: 返回对象的长度（元素个数）。实参可以是序列（如 string、bytes、tuple、list 或 range 等）或集合（如 dictionary、set 或 frozen set 等）。

class list([iterable])

Return a list whose items are the same and in the same order as iterable’s items. iterable may be either a sequence, a container that supports iteration, or an iterator object. If iterable is already a list, a copy is made and returned, similar to iterable[:]. For instance, list('abc') returns ['a', 'b', 'c'] and list( (1, 2, 3) ) returns [1, 2, 3]. If no argument is given, returns a new empty list, [].

list is a mutable sequence type, as documented in Sequence Types — str, unicode, list, tuple, bytearray, buffer, xrange. For other containers see the built in dict, set, and tuple classes, and the collections module.

locals()¶: Update and return a dictionary representing the current local symbol table. Free variables are returned by locals() when it is called in function blocks, but not in class blocks.

注解

不要更改此字典的内容；更改不会影响解释器使用的局部变量或自由变量的值。

class long(x=0)¶

class long(x, base=10)

Return a long integer object constructed from a string or number x. If the argument is a string, it must contain a possibly signed number of arbitrary size, possibly embedded in whitespace. The base argument is interpreted in the same way as for int(), and may only be given when x is a string. Otherwise, the argument may be a plain or long integer or a floating point number, and a long integer with the same value is returned. Conversion of floating point numbers to integers truncates (towards zero). If no arguments are given, returns 0L.

The long type is described in Numeric Types — int, float, long, complex.

map(function, iterable, ...)¶: Apply function to every item of iterable and return a list of the results. If additional iterable arguments are passed, function must take that many arguments and is applied to the items from all iterables in parallel. If one iterable is shorter than another it is assumed to be extended with None items. If function is None, the identity function is assumed; if there are multiple arguments, map() returns a list consisting of tuples containing the corresponding items from all iterables (a kind of transpose operation). The iterable arguments may be a sequence or any iterable object; the result is always a list.

max(iterable[, key])¶

max(arg1, arg2, *args[, key])

返回可迭代对象中最大的元素，或者返回两个及以上实参中最大的。

If one positional argument is provided, iterable must be a non-empty iterable (such as a non-empty string, tuple or list). The largest item in the iterable is returned. If two or more positional arguments are provided, the largest of the positional arguments is returned.

The optional key argument specifies a one-argument ordering function like that used for list.sort(). The key argument, if supplied, must be in keyword form (for example, max(a,b,c,key=func)).

在 2.5 版更改: Added support for the optional key argument.

memoryview(obj): 返回由给定实参创建的“内存视图”对象。有关详细信息，请参阅 memoryview type。

min(iterable[, key])¶

min(arg1, arg2, *args[, key])

返回可迭代对象中最小的元素，或者返回两个及以上实参中最小的。

If one positional argument is provided, iterable must be a non-empty iterable (such as a non-empty string, tuple or list). The smallest item in the iterable is returned. If two or more positional arguments are provided, the smallest of the positional arguments is returned.

The optional key argument specifies a one-argument ordering function like that used for list.sort(). The key argument, if supplied, must be in keyword form (for example, min(a,b,c,key=func)).

在 2.5 版更改: Added support for the optional key argument.

next(iterator[, default])¶: Retrieve the next item from the iterator by calling its next() method. If default is given, it is returned if the iterator is exhausted, otherwise StopIteration is raised.

2.6 新版功能.

class object¶: Return a new featureless object. object is a base for all new style classes. It has the methods that are common to all instances of new style classes.

2.2 新版功能.

在 2.3 版更改: This function does not accept any arguments. Formerly, it accepted arguments but ignored them.

oct(x)¶: Convert an integer number (of any size) to an octal string. The result is a valid Python expression.

在 2.4 版更改: Formerly only returned an unsigned literal.

open(name[, mode[, buffering]])¶

Open a file, returning an object of the file type described in section File Objects. If the file cannot be opened, IOError is raised. When opening a file, it’s preferable to use open() instead of invoking the file constructor directly.

The first two arguments are the same as for stdio’s fopen(): name is the file name to be opened, and mode is a string indicating how the file is to be opened.

The most commonly-used values of mode are 'r' for reading, 'w' for writing (truncating the file if it already exists), and 'a' for appending (which on some Unix systems means that all writes append to the end of the file regardless of the current seek position). If mode is omitted, it defaults to 'r'. The default is to use text mode, which may convert '\n' characters to a platform-specific representation on writing and back on reading. Thus, when opening a binary file, you should append 'b' to the mode value to open the file in binary mode, which will improve portability. (Appending 'b' is useful even on systems that don’t treat binary and text files differently, where it serves as documentation.) See below for more possible values of mode.

The optional buffering argument specifies the file’s desired buffer size: 0 means unbuffered, 1 means line buffered, any other positive value means use a buffer of (approximately) that size (in bytes). A negative buffering means to use the system default, which is usually line buffered for tty devices and fully buffered for other files. If omitted, the system default is used. [2]

Modes 'r+', 'w+' and 'a+' open the file for updating (reading and writing); note that 'w+' truncates the file. Append 'b' to the mode to open the file in binary mode, on systems that differentiate between binary and text files; on systems that don’t have this distinction, adding the 'b' has no effect.

In addition to the standard fopen() values mode may be 'U' or 'rU'. Python is usually built with universal newlines support; supplying 'U' opens the file as a text file, but lines may be terminated by any of the following: the Unix end-of-line convention '\n', the Macintosh convention '\r', or the Windows convention '\r\n'. All of these external representations are seen as '\n' by the Python program. If Python is built without universal newlines support a mode with 'U' is the same as normal text mode. Note that file objects so opened also have an attribute called newlines which has a value of None (if no newlines have yet been seen), '\n', '\r', '\r\n', or a tuple containing all the newline types seen.

Python enforces that the mode, after stripping 'U', begins with 'r', 'w' or 'a'.

Python provides many file handling modules including fileinput, os, os.path, tempfile, and shutil.

在 2.5 版更改: Restriction on first letter of mode string introduced.

ord(c)¶: Given a string of length one, return an integer representing the Unicode code point of the character when the argument is a unicode object, or the value of the byte when the argument is an 8-bit string. For example, ord('a') returns the integer 97, ord(u'\u2020') returns 8224. This is the inverse of chr() for 8-bit strings and of unichr() for unicode objects. If a unicode argument is given and Python was built with UCS2 Unicode, then the character’s code point must be in the range [0..65535] inclusive; otherwise the string length is two, and a TypeError will be raised.

pow(x, y[, z])¶

返回 x 的 y 次幂；如果 z 存在，则对 z 取余（比直接 pow(x, y) % z 计算更高效）。两个参数形式的 pow(x, y) 等价于幂运算符： x**y。

The arguments must have numeric types. With mixed operand types, the coercion rules for binary arithmetic operators apply. For int and long int operands, the result has the same type as the operands (after coercion) unless the second argument is negative; in that case, all arguments are converted to float and a float result is delivered. For example, 10**2 returns 100, but 10**-2 returns 0.01. (This last feature was added in Python 2.2. In Python 2.1 and before, if both arguments were of integer types and the second argument was negative, an exception was raised.) If the second argument is negative, the third argument must be omitted. If z is present, x and y must be of integer types, and y must be non-negative. (This restriction was added in Python 2.2. In Python 2.1 and before, floating 3-argument pow() returned platform-dependent results depending on floating-point rounding accidents.)

print(*objects, sep=' ', end='\n', file=sys.stdout)¶

Print objects to the stream file, separated by sep and followed by end. sep, end and file, if present, must be given as keyword arguments.

所有非关键字参数都会被转换为字符串，就像是执行了 str() 一样，并会被写入到流，以 sep 且在末尾加上 end。 sep 和 end 都必须为字符串；它们也可以为 None，这意味着使用默认值。如果没有给出 objects，则 print() 将只写入 end。

The file argument must be an object with a write(string) method; if it is not present or None, sys.stdout will be used. Output buffering is determined by file. Use file.flush() to ensure, for instance, immediate appearance on a screen.

注解

This function is not normally available as a built-in since the name print is recognized as the print statement. To disable the statement and use the print() function, use this future statement at the top of your module:

from __future__ import print_function

2.6 新版功能.

class property([fget[, fset[, fdel[, doc]]]])¶

Return a property attribute for new-style classes (classes that derive from object).

fget 是获取属性值的函数。 fset 是用于设置属性值的函数。 fdel 是用于删除属性值的函数。并且 doc 为属性对象创建文档字符串。

一个典型的用法是定义一个托管属性 x:

class C(object):
    def __init__(self):
        self._x = None

    def getx(self):
        return self._x

    def setx(self, value):
        self._x = value

    def delx(self):
        del self._x

    x = property(getx, setx, delx, "I'm the 'x' property.")

如果 c 是 C 的实例，c.x 将调用getter，c.x = value 将调用setter， del c.x 将调用deleter。

如果给出，doc 将成为该 property 属性的文档字符串。否则该 property 将拷贝 fget 的文档字符串（如果存在）。这令使用 property() 作为 decorator 来创建只读的特征属性可以很容易地实现:

class Parrot(object):
    def __init__(self):
        self._voltage = 100000

    @property
    def voltage(self):
        """Get the current voltage."""
        return self._voltage

以上 @property 装饰器会将 voltage() 方法转化为一个具有相同名称的只读属性的 “getter”，并将 voltage 的文档字符串设置为 “Get the current voltage.”

特征属性对象具有 getter, setter 以及 deleter 方法，它们可用作装饰器来创建该特征属性的副本，并将相应的访问函数设为所装饰的函数。这最好是用一个例子来解释:

class C(object):
    def __init__(self):
        self._x = None

    @property
    def x(self):
        """I'm the 'x' property."""
        return self._x

    @x.setter
    def x(self, value):
        self._x = value

    @x.deleter
    def x(self):
        del self._x

上述代码与第一个例子完全等价。注意一定要给附加函数与原始的特征属性相同的名称 (在本例中为 x。)

返回的特征属性对象同样具有与构造器参数相对应的属性 fget, fset 和 fdel。

2.2 新版功能.

在 2.5 版更改: Use fget’s docstring if no doc given.

在 2.6 版更改: The getter, setter, and deleter attributes were added.

range(stop)¶

range(start, stop[, step])

This is a versatile function to create lists containing arithmetic progressions. It is most often used in for loops. The arguments must be plain integers. If the step argument is omitted, it defaults to 1. If the start argument is omitted, it defaults to 0. The full form returns a list of plain integers [start, start + step, start + 2 * step, ...]. If step is positive, the last element is the largest start + i * step less than stop; if step is negative, the last element is the smallest start + i * step greater than stop. step must not be zero (or else ValueError is raised). Example:

>>> range(10)
[0, 1, 2, 3, 4, 5, 6, 7, 8, 9]
>>> range(1, 11)
[1, 2, 3, 4, 5, 6, 7, 8, 9, 10]
>>> range(0, 30, 5)
[0, 5, 10, 15, 20, 25]
>>> range(0, 10, 3)
[0, 3, 6, 9]
>>> range(0, -10, -1)
[0, -1, -2, -3, -4, -5, -6, -7, -8, -9]
>>> range(0)
[]
>>> range(1, 0)
[]

raw_input([prompt])¶

If the prompt argument is present, it is written to standard output without a trailing newline. The function then reads a line from input, converts it to a string (stripping a trailing newline), and returns that. When EOF is read, EOFError is raised. Example:

>>> s = raw_input('--> ')
--> Monty Python's Flying Circus
>>> s
"Monty Python's Flying Circus"

If the readline module was loaded, then raw_input() will use it to provide elaborate line editing and history features.

reduce(function, iterable[, initializer])¶

Apply function of two arguments cumulatively to the items of iterable, from left to right, so as to reduce the iterable to a single value. For example, reduce(lambda x, y: x+y, [1, 2, 3, 4, 5]) calculates ((((1+2)+3)+4)+5). The left argument, x, is the accumulated value and the right argument, y, is the update value from the iterable. If the optional initializer is present, it is placed before the items of the iterable in the calculation, and serves as a default when the iterable is empty. If initializer is not given and iterable contains only one item, the first item is returned. Roughly equivalent to:

def reduce(function, iterable, initializer=None):
    it = iter(iterable)
    if initializer is None:
        try:
            initializer = next(it)
        except StopIteration:
            raise TypeError('reduce() of empty sequence with no initial value')
    accum_value = initializer
    for x in it:
        accum_value = function(accum_value, x)
    return accum_value

reload(module)¶

Reload a previously imported module. The argument must be a module object, so it must have been successfully imported before. This is useful if you have edited the module source file using an external editor and want to try out the new version without leaving the Python interpreter. The return value is the module object (the same as the module argument).

When reload(module) is executed:

Python modules’ code is recompiled and the module-level code reexecuted, defining a new set of objects which are bound to names in the module’s dictionary. The init function of extension modules is not called a second time.
As with all other objects in Python the old objects are only reclaimed after their reference counts drop to zero.
The names in the module namespace are updated to point to any new or changed objects.
Other references to the old objects (such as names external to the module) are not rebound to refer to the new objects and must be updated in each namespace where they occur if that is desired.

There are a number of other caveats:

When a module is reloaded, its dictionary (containing the module’s global variables) is retained. Redefinitions of names will override the old definitions, so this is generally not a problem. If the new version of a module does not define a name that was defined by the old version, the old definition remains. This feature can be used to the module’s advantage if it maintains a global table or cache of objects — with a try statement it can test for the table’s presence and skip its initialization if desired:

try:
    cache
except NameError:
    cache = {}

It is generally not very useful to reload built-in or dynamically loaded modules. Reloading sys, __main__, builtins and other key modules is not recommended. In many cases extension modules are not designed to be initialized more than once, and may fail in arbitrary ways when reloaded.

If a module imports objects from another module using from … import …, calling reload() for the other module does not redefine the objects imported from it — one way around this is to re-execute the from statement, another is to use import and qualified names (module.*name*) instead.

If a module instantiates instances of a class, reloading the module that defines the class does not affect the method definitions of the instances — they continue to use the old class definition. The same is true for derived classes.

repr(object)¶: Return a string containing a printable representation of an object. This is the same value yielded by conversions (reverse quotes). It is sometimes useful to be able to access this operation as an ordinary function. For many types, this function makes an attempt to return a string that would yield an object with the same value when passed to eval(), otherwise the representation is a string enclosed in angle brackets that contains the name of the type of the object together with additional information often including the name and address of the object. A class can control what this function returns for its instances by defining a __repr__() method.

reversed(seq)¶: 返回一个反向的 iterator。 seq 必须是一个具有 __reversed__() 方法的对象或者是支持该序列协议（具有从``0`` 开始的整数类型参数的 __len__() 方法和 __getitem__() 方法）。

2.4 新版功能.

在 2.6 版更改: Added the possibility to write a custom __reversed__() method.

round(number[, ndigits])¶: Return the floating point value number rounded to ndigits digits after the decimal point. If ndigits is omitted, it defaults to zero. The result is a floating point number. Values are rounded to the closest multiple of 10 to the power minus ndigits; if two multiples are equally close, rounding is done away from 0 (so, for example, round(0.5) is 1.0 and round(-0.5) is -1.0).

注解

对浮点数执行 round() 的行为可能会令人惊讶：例如，round(2.675, 2) 将给出 2.67 而不是期望的 2.68。这不算是程序错误：这一结果是由于大多数十进制小数实际上都不能以浮点数精确地表示。请参阅浮点算术：争议和限制了解更多信息。

class set([iterable])

返回一个新的 set 对象，可以选择带有从 iterable 获取的元素。 set 是一个内置类型。请查看 set 和集合类型 — set, frozenset 获取关于这个类的文档。

有关其他容器请参看内置的 frozenset, list, tuple 和 dict 类，以及 collections 模块。

2.4 新版功能.

setattr(object, name, value)¶: 此函数与 getattr() 两相对应。其参数为一个对象、一个字符串和一个任意值。字符串指定一个现有属性或者新增属性。函数会将值赋给该属性，只要对象允许这种操作。例如，setattr(x, 'foobar', 123) 等价于 x.foobar = 123。

class slice(stop)¶
class slice(start, stop[, step]): 返回一个表示由 range(start, stop, step) 所指定索引集的 slice 对象。其中 start 和 step 参数默认为 None。切片对象具有仅会返回对应参数值（或其默认值）的只读数据属性 start, stop 和 step。它们没有其他的显式功能；不过它们会被 NumPy 以及其他第三方扩展所使用。切片对象也会在使用扩展索引语法时被生成。例如: a[start:stop:step] 或 a[start:stop, i]。请参阅 itertools.islice() 了解返回迭代器的一种替代版本。

sorted(iterable[, cmp[, key[, reverse]]])¶

根据 iterable 中的项返回一个新的已排序列表。

The optional arguments cmp, key, and reverse have the same meaning as those for the list.sort() method (described in section 可变序列类型).

cmp specifies a custom comparison function of two arguments (iterable elements) which should return a negative, zero or positive number depending on whether the first argument is considered smaller than, equal to, or larger than the second argument: cmp=lambda x,y: cmp(x.lower(), y.lower()). The default value is None.

key specifies a function of one argument that is used to extract a comparison key from each list element: key=str.lower. The default value is None (compare the elements directly).

reverse 为一个布尔值。如果设为 True，则每个列表元素将按反向顺序比较进行排序。

In general, the key and reverse conversion processes are much faster than specifying an equivalent cmp function. This is because cmp is called multiple times for each list element while key and reverse touch each element only once. Use functools.cmp_to_key() to convert an old-style cmp function to a key function.

内置的 sorted() 确保是稳定的。如果一个排序确保不会改变比较结果相等的元素的相对顺序就称其为稳定的 — 这有利于进行多重排序（例如先按部门、再按薪级排序）。

有关排序示例和简要排序教程，请参阅排序指南。

2.4 新版功能.

staticmethod(function)¶

Return a static method for function.

静态方法不会接收隐式的第一个参数。要声明一个静态方法，请使用此语法

class C(object):
    @staticmethod
    def f(arg1, arg2, ...):
        ...

@staticmethod 这样的形式称为函数的 decorator – 详情参阅函数定义。

静态方法的调用可以在类上进行 (例如 C.f()) 也可以在实例上进行 (例如 C().f())。

Python中的静态方法与Java或C ++中的静态方法类似。另请参阅 classmethod() ，用于创建备用类构造函数的变体。

想了解更多有关静态方法的信息，请参阅标准类型层级结构。

2.2 新版功能.

在 2.4 版更改: Function decorator syntax added.

class str(object='')¶

Return a string containing a nicely printable representation of an object. For strings, this returns the string itself. The difference with repr(object) is that str(object) does not always attempt to return a string that is acceptable to eval(); its goal is to return a printable string. If no argument is given, returns the empty string, ''.

For more information on strings see Sequence Types — str, unicode, list, tuple, bytearray, buffer, xrange which describes sequence functionality (strings are sequences), and also the string-specific methods described in the 字符串的方法 section. To output formatted strings use template strings or the % operator described in the String Formatting Operations section. In addition see the String Services section. See also unicode().

sum(iterable[, start])¶

从 start 开始自左向右对 iterable 中的项求和并返回总计值。 start 默认为 0。 iterable 的项通常为数字，开始值则不允许为字符串。

对某些用例来说，存在 sum() 的更好替代。拼接字符串序列的更好更快方式是调用 ''.join(sequence)。要以扩展精度对浮点值求和，请参阅 math.fsum()。要拼接一系列可迭代对象，请考虑使用 itertools.chain()。

2.3 新版功能.

super(type[, object-or-type])¶

返回一个代理对象，它会将方法调用委托给 type 指定的父类或兄弟类。这对于访问已在类中被重载的继承方法很有用。搜索顺序与 getattr() 所使用的相同，只是 type 指定的类型本身会被跳过。

type 的 __mro__ 属性列出了 getattr() 和 super() 所使用的方法解析顺序。该属性是动态的，可以在继承层级结构更新的时候任意改变。

如果省略第二个参数，则返回的超类对象是未绑定的。如果第二个参数为一个对象，则 isinstance(obj, type) 必须为真值。如果第二个参数为一个类型，则 issubclass(type2, type) 必须为真值（这适用于类方法）。

注解

super() only works for new-style classes.

super 有两个典型用例。在具有单继承的类层级结构中，super 可用来引用父类而不必显式地指定它们的名称，从而令代码更易维护。这种用法与其他编程语言中 super 的用法非常相似。

第二个用例是在动态执行环境中支持协作多重继承。此用例为 Python 所独有，在静态编译语言或仅支持单继承的语言中是不存在的。这使得实现“菱形图”成为可能，在这时会有多个基类实现相同的方法。好的设计强制要求这种方法在每个情况下具有相同的调用签名（因为调用顺序是在运行时确定的，也因为该顺序要适应类层级结构的更改，还因为该顺序可能包含在运行时之前未知的兄弟类）。

对于以上两个用例，典型的超类调用看起来是这样的:

class C(B):
    def method(self, arg):
        super(C, self).method(arg)

请注意 super() 是作为显式加点属性查找的绑定过程的一部分来实现的，例如 super().__getitem__(name)。它做到这一点是通过实现自己的 __getattribute__() 方法，这样就能以可预测的顺序搜索类，并且支持协作多重继承。对应地，super() 在像 super()[name] 这样使用语句或操作符进行隐式查找时则未被定义。

Also note that super() is not limited to use inside methods. The two argument form specifies the arguments exactly and makes the appropriate references.

对于有关如何使用 super() 来如何设计协作类的实用建议，请参阅使用 super() 的指南。

2.2 新版功能.

tuple([iterable])¶

Return a tuple whose items are the same and in the same order as iterable’s items. iterable may be a sequence, a container that supports iteration, or an iterator object. If iterable is already a tuple, it is returned unchanged. For instance, tuple('abc') returns ('a', 'b', 'c') and tuple([1, 2, 3]) returns (1, 2, 3). If no argument is given, returns a new empty tuple, ().

tuple is an immutable sequence type, as documented in Sequence Types — str, unicode, list, tuple, bytearray, buffer, xrange. For other containers see the built in dict, list, and set classes, and the collections module.

class type(object)¶

class type(name, bases, dict)

With one argument, return the type of an object. The return value is a type object. The isinstance() built-in function is recommended for testing the type of an object.

With three arguments, return a new type object. This is essentially a dynamic form of the class statement. The name string is the class name and becomes the __name__ attribute; the bases tuple itemizes the base classes and becomes the __bases__ attribute; and the dict dictionary is the namespace containing definitions for class body and becomes the __dict__ attribute. For example, the following two statements create identical type objects:

>>> class X(object):
...     a = 1
...
>>> X = type('X', (object,), dict(a=1))

2.2 新版功能.

unichr(i)¶: Return the Unicode string of one character whose Unicode code is the integer i. For example, unichr(97) returns the string u'a'. This is the inverse of ord() for Unicode strings. The valid range for the argument depends how Python was configured – it may be either UCS2 [0..0xFFFF] or UCS4 [0..0x10FFFF]. ValueError is raised otherwise. For ASCII and 8-bit strings see chr().

2.0 新版功能.

unicode(object='')¶

unicode(object[, encoding[, errors]])

Return the Unicode string version of object using one of the following modes:

If encoding and/or errors are given, unicode() will decode the object which can either be an 8-bit string or a character buffer using the codec for encoding. The encoding parameter is a string giving the name of an encoding; if the encoding is not known, LookupError is raised. Error handling is done according to errors; this specifies the treatment of characters which are invalid in the input encoding. If errors is 'strict' (the default), a ValueError is raised on errors, while a value of 'ignore' causes errors to be silently ignored, and a value of 'replace' causes the official Unicode replacement character, U+FFFD, to be used to replace input characters which cannot be decoded. See also the codecs module.

If no optional parameters are given, unicode() will mimic the behaviour of str() except that it returns Unicode strings instead of 8-bit strings. More precisely, if object is a Unicode string or subclass it will return that Unicode string without any additional decoding applied.

For objects which provide a __unicode__() method, it will call this method without arguments to create a Unicode string. For all other objects, the 8-bit string version or representation is requested and then converted to a Unicode string using the codec for the default encoding in 'strict' mode.

For more information on Unicode strings see Sequence Types — str, unicode, list, tuple, bytearray, buffer, xrange which describes sequence functionality (Unicode strings are sequences), and also the string-specific methods described in the 字符串的方法 section. To output formatted strings use template strings or the % operator described in the String Formatting Operations section. In addition see the String Services section. See also str().

2.0 新版功能.

在 2.2 版更改: Support for __unicode__() added.

vars([object])¶

返回模块、类、实例或任何其它具有 __dict__ 属性的对象的 __dict__ 属性。

Objects such as modules and instances have an updateable __dict__ attribute; however, other objects may have write restrictions on their __dict__ attributes (for example, new-style classes use a dictproxy to prevent direct dictionary updates).

不带参数时，vars() 的行为类似 locals()。请注意，locals 字典仅对于读取起作用，因为对 locals 字典的更新会被忽略。

xrange(stop)¶
xrange(start, stop[, step]): This function is very similar to range(), but returns an xrange object instead of a list. This is an opaque sequence type which yields the same values as the corresponding list, without actually storing them all simultaneously. The advantage of xrange() over range() is minimal (since xrange() still has to create the values when asked for them) except when a very large range is used on a memory-starved machine or when all of the range’s elements are never used (such as when the loop is usually terminated with break). For more information on xrange objects, see XRange Type and Sequence Types — str, unicode, list, tuple, bytearray, buffer, xrange.

CPython implementation detail: xrange() is intended to be simple and fast. Implementations may impose restrictions to achieve this. The C implementation of Python restricts all arguments to native C longs (“short” Python integers), and also requires that the number of elements fit in a native C long. If a larger range is needed, an alternate version can be crafted using the itertools module: islice(count(start, step), (stop-start+step-1+2*(step<0))//step).

zip([iterable, ...])¶

This function returns a list of tuples, where the i-th tuple contains the i-th element from each of the argument sequences or iterables. The returned list is truncated in length to the length of the shortest argument sequence. When there are multiple arguments which are all of the same length, zip() is similar to map() with an initial argument of None. With a single sequence argument, it returns a list of 1-tuples. With no arguments, it returns an empty list.

The left-to-right evaluation order of the iterables is guaranteed. This makes possible an idiom for clustering a data series into n-length groups using zip(*[iter(s)]*n).

zip() 与 * 运算符相结合可以用来拆解一个列表:

>>> x = [1, 2, 3]
>>> y = [4, 5, 6]
>>> zipped = zip(x, y)
>>> zipped
[(1, 4), (2, 5), (3, 6)]
>>> x2, y2 = zip(*zipped)
>>> x == list(x2) and y == list(y2)
True

2.0 新版功能.

在 2.4 版更改: Formerly, zip() required at least one argument and zip() raised a TypeError instead of returning an empty list.

__import__(name[, globals[, locals[, fromlist[, level]]]])¶

注解

与 importlib.import_module() 不同，这是一个日常 Python 编程中不需要用到的高级函数。

This function is invoked by the import statement. It can be replaced (by importing the __builtin__ module and assigning to __builtin__.__import__) in order to change semantics of the import statement, but nowadays it is usually simpler to use import hooks (see PEP 302). Direct use of __import__() is rare, except in cases where you want to import a module whose name is only known at runtime.

该函数会导入 name 模块，有可能使用给定的 globals 和 locals 来确定如何在包的上下文中解读名称。 fromlist 给出了应该从由 name 指定的模块导入对象或子模块的名称。标准实现完全不使用其 locals 参数，而仅使用 globals 参数来确定 import 语句的包上下文。

level specifies whether to use absolute or relative imports. The default is -1 which indicates both absolute and relative imports will be attempted. 0 means only perform absolute imports. Positive values for level indicate the number of parent directories to search relative to the directory of the module calling __import__().

当 name 变量的形式为 package.module 时，通常将会返回最高层级的包（第一个点号之前的名称），而不是以 name 命名的模块。但是，当给出了非空的 fromlist 参数时，则将返回以 name 命名的模块。

例如，语句 import spam 的结果将为与以下代码作用相同的字节码:

spam = __import__('spam', globals(), locals(), [], -1)

语句 import spam.ham 的结果将为以下调用:

spam = __import__('spam.ham', globals(), locals(), [], -1)

请注意在这里 __import__() 是如何返回顶层模块的，因为这是通过 import 语句被绑定到特定名称的对象。

另一方面，语句 from spam.ham import eggs, sausage as saus 的结果将为

_temp = __import__('spam.ham', globals(), locals(), ['eggs', 'sausage'], -1)
eggs = _temp.eggs
saus = _temp.sausage

在这里， spam.ham 模块会由 __import__() 返回。要导入的对象将从此对象中提取并赋值给它们对应的名称。

如果您只想按名称导入模块（可能在包中），请使用 importlib.import_module()

在 2.5 版更改: The level parameter was added.

在 2.5 版更改: Keyword support for parameters was added.

3. Non-essential Built-in Functions¶

There are several built-in functions that are no longer essential to learn, know or use in modern Python programming. They have been kept here to maintain backwards compatibility with programs written for older versions of Python.

Python programmers, trainers, students and book writers should feel free to bypass these functions without concerns about missing something important.

apply(function, args[, keywords])¶: The function argument must be a callable object (a user-defined or built-in function or method, or a class object) and the args argument must be a sequence. The function is called with args as the argument list; the number of arguments is the length of the tuple. If the optional keywords argument is present, it must be a dictionary whose keys are strings. It specifies keyword arguments to be added to the end of the argument list. Calling apply() is different from just calling function(args), since in that case there is always exactly one argument. The use of apply() is equivalent to function(*args, **keywords).

2.3 版后已移除: Use function(*args, **keywords) instead of apply(function, args, keywords) (see 解包参数列表).

buffer(object[, offset[, size]])¶: The object argument must be an object that supports the buffer call interface (such as strings, arrays, and buffers). A new buffer object will be created which references the object argument. The buffer object will be a slice from the beginning of object (or from the specified offset). The slice will extend to the end of object (or will have a length given by the size argument).

coerce(x, y)¶: Return a tuple consisting of the two numeric arguments converted to a common type, using the same rules as used by arithmetic operations. If coercion is not possible, raise TypeError.

intern(string)¶: Enter string in the table of “interned” strings and return the interned string – which is string itself or a copy. Interning strings is useful to gain a little performance on dictionary lookup – if the keys in a dictionary are interned, and the lookup key is interned, the key comparisons (after hashing) can be done by a pointer compare instead of a string compare. Normally, the names used in Python programs are automatically interned, and the dictionaries used to hold module, class or instance attributes have interned keys.

在 2.3 版更改: Interned strings are not immortal (like they used to be in Python 2.2 and before); you must keep a reference to the return value of intern() around to benefit from it.

脚注

[1]	It is used relatively rarely so does not warrant being made into a statement.

[2] Specifying a buffer size currently has no effect on systems that don’t have setvbuf(). The interface to specify the buffer size is not done using a method that calls setvbuf(), because that may dump core when called after any I/O has been performed, and there’s no reliable way to determine whether this is the case.

[3]	In the current implementation, local variable bindings cannot normally be affected this way, but variables retrieved from other scopes (such as modules) can be. This may change.

2. 内置函数¶

3. Non-essential Built-in Functions¶

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