Python学习笔记(三):常用内置函数学习

一.如何查看Python3的所有内置函数

命令：dir(__builtins__)

效果如下：

dir(__builtins__)

['ArithmeticError', 'AssertionError', 'AttributeError', 'BaseException',

'BlockingIOError', 'BrokenPipeError', 'BufferError', 'BytesWarning',

'ChildProcessError', 'ConnectionAbortedError', 'ConnectionError',

'ConnectionRefusedError', 'ConnectionResetError', 'DeprecationWarning', 'EOFError',

'Ellipsis', 'EnvironmentError', 'Exception', 'False', 'FileExistsError',

'FileNotFoundError', 'FloatingPointError', 'FutureWarning', 'GeneratorExit', 'IOError',

'ImportError', 'ImportWarning', 'IndentationError', 'IndexError', 'InterruptedError',

'IsADirectoryError', 'KeyError', 'KeyboardInterrupt', 'LookupError', 'MemoryError',

'NameError', 'None', 'NotADirectoryError', 'NotImplemented', 'NotImplementedError',

'OSError', 'OverflowError', 'PendingDeprecationWarning', 'PermissionError',

'ProcessLookupError', 'ReferenceError', 'ResourceWarning', 'RuntimeError',

'RuntimeWarning', 'StopIteration', 'SyntaxError', 'SyntaxWarning', 'SystemError',

'SystemExit', 'TabError', 'TimeoutError', 'True', 'TypeError', 'UnboundLocalError',

'UnicodeDecodeError', 'UnicodeEncodeError', 'UnicodeError', 'UnicodeTranslateError',

'UnicodeWarning', 'UserWarning', 'ValueError', 'Warning', 'WindowsError',

'ZeroDivisionError', '__build_class__', '__debug__', '__doc__', '__import__',

'__loader__', '__name__', '__package__', '__spec__', 'abs', 'all', 'any', 'ascii',

'bin', 'bool', 'bytearray', 'bytes', 'callable', 'chr', 'classmethod', 'compile',

'complex', 'copyright', 'credits', 'delattr', 'dict', 'dir', 'divmod', 'enumerate',

'eval', 'exec', 'exit', 'filter', 'float', 'format', 'frozenset', 'getattr', 'globals',

'hasattr', 'hash', 'help', 'hex', 'id', 'input', 'int', 'isinstance', 'issubclass',

'iter', 'len', 'license', 'list', 'locals', 'map', 'max', 'memoryview', 'min', 'next',

'object', 'oct', 'open', 'ord', 'pow', 'print', 'property', 'quit', 'range', 'repr',

'reversed', 'round', 'set', 'setattr', 'slice', 'sorted', 'staticmethod', 'str', 'sum',

'super', 'tuple', 'type', 'vars', 'zip']

二.如何使用内置函数.

help(内置函数) 或者百度或者Google

三.常用内置函数介绍。

1.chr和ord

help(chr)

Help on built-in function chr in module builtins:

chr(...)

    chr(i) -> Unicode character

    

    Return a Unicode string of one character with ordinal i; 0 <= i <= 0x10ffff.

chr只有一个ordinal参数，并且范围是[0,10FFFF]

功能：将参数i转换为Unicode 字符

In [1]: chr(0)
Out[1]: '\x00'

In [2]: chr(0x31)
Out[2]: '1'

In [3]: chr(65)
Out[3]: 'A'

In [4]: chr(20013)
Out[4]: '中'

>>> help(ord)

Help on built-in function ord in module builtins:

ord(...)

    ord(c) -> integer

    

    Return the integer ordinal of a one-character string.

chr只有一个ordinal参数，并且必须是单个字符

功能：将Unicode 字符转换为整数

In [6]: ord('0')
Out[6]: 48

In [7]: ord('A')
Out[7]: 65

In [8]: ord('a')
Out[8]: 97

In [9]: ord('中')
Out[9]: 20013

2.min和max

>>> help(min)

Help on built-in function min in module builtins:

min(...)

    min(iterable, *[, default=obj, key=func]) -> value

    min(arg1, arg2, *args, *[, key=func]) -> value

    

    With a single iterable argument, return its smallest item. The

    default keyword-only argument specifies an object to return if

    the provided iterable is empty.

    With two or more arguments, return the smallest argument.

两种函数形式，参数可以是迭代器，也可以至少两个参数，返回最小的一个

功能:返回参数里最小的一个对象。

In [11]: min('a','b','c')   #必须是同一类型的参数
Out[11]: 'a'

In [12]: min(-5,-100,99,25)
Out[12]: -100

In [13]: list = [1,3,5,7,9,-11]

In [14]: min(list)   #参数是可迭代的对象
Out[14]: -11

In [15]: min(-5,-100,99,25,key = abs)  #可以指定方式比较
Out[15]: -5

In [16]: min(-5,-100,99,25,key = lambda x:x**2)  #包含lambda语句
Out[16]: -5

>>> help(max)

Help on built-in function max in module builtins:

max(...)

    max(iterable, *[, default=obj, key=func]) -> value

    max(arg1, arg2, *args, *[, key=func]) -> value

    

    With a single iterable argument, return its biggest item. The

    default keyword-only argument specifies an object to return if

    the provided iterable is empty.

    With two or more arguments, return the largest argument.

参数和min函数是一样的，求最大值。

In [17]: max('a','b','c')  #必须是同一类型的参数
Out[17]: 'c'

In [18]: max(-5,-100,99,25)
Out[18]: 99

In [19]: list = [1,3,5,7,9,-11]

In [20]: max(list)   #参数是可迭代的对象
Out[20]: 9

In [21]: max(-5,-100,99,25,key = abs)  #可以指定方式比较
Out[21]: -100

In [22]: max(-5,-100,99,25,key = lambda x:x**2)  #包含lambda语句
Out[22]: -100

3.bin、hex和oct

>>> help(bin)

Help on built-in function bin in module builtins:

bin(...)

    bin(number) -> string

    

    Return the binary representation of an integer.

    

       >>> bin(2796202)

       '0b1010101010101010101010'

将一个integer转换为二进制形式，返回字符串。

In [23]: bin(7)
Out[23]: '0b111'

In [24]: bin(123)
Out[24]: '0b1111011'

In [25]: bin(2796202)
Out[25]: '0b1010101010101010101010'

>>> help(oct)

Help on built-in function oct in module builtins:

oct(...)

    oct(number) -> string

    

    Return the octal representation of an integer.

    

       >>> oct(342391)

       '0o1234567'

将一个integer转换为八进制形式，返回字符串

In [26]: oct(7)
Out[26]: '0o7'

In [27]: oct(8)
Out[27]: '0o10'

In [28]: oct(123)
Out[28]: '0o173'

In [29]: oct(342391)
Out[29]: '0o1234567'

>>> help(hex)

Help on built-in function hex in module builtins:

hex(...)

    hex(number) -> string

    

    Return the hexadecimal representation of an integer.

    

       >>> hex(3735928559)

       '0xdeadbeef'

将一个integer转换为十六进制形式，返回字符串

In [30]: hex(7)
Out[30]: '0x7'

In [31]: hex(123)
Out[31]: '0x7b'

In [32]: hex(15)
Out[32]: '0xf'

In [33]: hex(3735928559)
Out[33]: '0xdeadbeef'

4.abs和sum

>>> help(abs)

Help on built-in function abs in module builtins:

abs(...)

    abs(number) -> number

    

    Return the absolute value of the argument.

求绝对值

In [38]: abs(5)
Out[38]: 5

In [39]: abs(-5)
Out[39]: 5

In [40]: abs(0)
Out[40]: 0

In [41]: abs(-567)
Out[41]: 567

In [42]: abs(-56.7)
Out[42]: 56.7

>>> help(sum)

Help on built-in function sum in module builtins:

sum(...)

    sum(iterable[, start]) -> value

    

    Return the sum of an iterable of numbers (NOT strings) plus the value

    of parameter 'start' (which defaults to 0).  When the iterable is

    empty, return start.

sum的参数是一个可迭代对象。而且可迭代器对象里的item不能是字符串，必须是数字。

In [45]: L = [1,2,3,4,5]

In [46]: sum(L)
Out[46]: 15

In [47]: T = 1,2,3,4,5

In [48]: sum(T)
Out[48]: 15

In [49]: S = {1,2,3,4,5}

In [50]: sum(S)
Out[50]: 15

In [51]: sum(S,2)
Out[51]: 17

In [52]: sum(S,-2)
Out[52]: 13

5.divmod、pow和round

>>> help(divmod)

Help on built-in function divmod in module builtins:

divmod(...)

    divmod(x, y) -> (div, mod)

    

    Return the tuple ((x-x%y)/y, x%y).  Invariant: div*y + mod == x.

两个参数，返回商和余数(tuple类型)

In [57]: divmod(12,3.2)
Out[57]: (3.0, 2.3999999999999995)

In [58]: divmod(12,3)
Out[58]: (4, 0)

In [59]: divmod(12,5)
Out[59]: (2, 2)

In [60]: divmod(5,12)
Out[60]: (0, 5)

In [61]: divmod(12,3.5)
Out[61]: (3.0, 1.5)

In [62]: divmod(12,3.7)
Out[62]: (3.0, 0.8999999999999995)

In [63]: divmod(12.6,3.7)
Out[63]: (3.0, 1.4999999999999991)

>>> help(pow)

Help on built-in function pow in module builtins:

pow(...)

    pow(x, y[, z]) -> number

    

    With two arguments, equivalent to x**y.  With three arguments,

    equivalent to (x**y) % z, but may be more efficient (e.g. for ints).

如果是2个参数，则返回X的Y次方

如果是3个参数，则返回X的Y次方 除以 Z 的余数

三个参数都必须是整数

In [64]: pow(2,2,3)    #2*2 % 3 = 1
Out[64]: 1

In [65]: pow(2,2)  # 2*2 = 4
Out[65]: 4

In [66]: pow(2,5)  # 2*2*2*2*2 = 32
Out[66]: 32

In [67]: pow(2,5,6)  # 2*2*2*2*2 % 6 = 2
Out[67]: 2

>>> help(round)

Help on built-in function round in module builtins:

round(...)

    round(number[, ndigits]) -> number

    

    Round a number to a given precision in decimal digits (default 0 digits).

    This returns an int when called with one argument, otherwise the

    same type as the number. ndigits may be negative.

四舍五入，可指定精度，默认取整

In [70]: round(1.23)
Out[70]: 1

In [71]: round(1.56)
Out[71]: 2

In [72]: round(1.56789,3)
Out[72]: 1.568

In [73]: round(1.56789,6)
Out[73]: 1.56789

In [74]: round(1.56789,8)
Out[74]: 1.56789

In [75]: round(1.56789,-8)
Out[75]: 0.0

In [76]: round(2/3,6)
Out[76]: 0.666667

6.all和any

>>> help(all)

Help on built-in function all in module builtins:

all(...)

    all(iterable) -> bool

    

    Return True if bool(x) is True for all values x in the iterable.

    If the iterable is empty, return True.

参数：迭代器。

包含0值，返回False，否则返回True

迭代器为空，返回True

In [77]: L = [1,3,2,7,9,0]

In [78]: all(L)
Out[78]: False

In [79]: L = [1,3,2,7,9]

In [80]: all(L)
Out[80]: True

In [81]: L = [1,3,2,7,9,None]

In [82]: all(L)
Out[82]: False

In [83]: L = [1,3,2,7,9,'']

In [84]: all(L)
Out[84]: False

In [85]: L = [1,3,2,7,9,' ']

In [86]: all(L)
Out[86]: True

In [87]: L = []

In [88]: all(L)   #迭代器为空，返回True
Out[88]: True

>>> help(any)

Help on built-in function any in module builtins:

any(...)

    any(iterable) -> bool

    

    Return True if bool(x) is True for any x in the iterable.

    If the iterable is empty, return False.

参数：迭代器。

包含非0值，返回True，否则返回False

迭代器为空，返回False

In [96]: L = ['',2,3]

In [97]: any(L)
Out[97]: True

In [98]: L = ['',[],{}]

In [99]: any(L)
Out[99]: False

In [100]: L = ['',[],{},'0']

In [101]: any(L)
Out[101]: True

In [102]: L = ['',[],{},0]

In [103]: any(L)
Out[103]: False

7.ascii

>>> help(ascii)

Help on built-in function ascii in module builtins:

ascii(...)

    ascii(object) -> string

    

    As repr(), return a string containing a printable representation of an

    object, but escape the non-ASCII characters in the string returned by

    repr() using \x, \u or \U escapes.  This generates a string similar

    to that returned by repr() in Python 2.

返回对象的可打印表字符串表现方式

In [104]: ascii('!')
Out[104]: "'!'"

In [105]: ascii(1)
Out[105]: '1'

In [106]: ascii('1')
Out[106]: "'1'"

In [107]: ascii(123456)
Out[107]: '123456'

In [108]: ascii('中国')
Out[108]: "'\\u4e2d\\u56fd'"

In [109]: ascii('\n')
Out[109]: "'\\n'"

IIn [110]: ascii('□')
Out[110]: "'\\u25a1'"

InIn [112]: ascii('×')
Out[112]: "'\\xd7'"

In [113]: print ('\xd7')
×

8.input

>>> help(input)

Help on built-in function input in module builtins:

input(...)

    input([prompt]) -> string

    

    Read a string from standard input.  The trailing newline is stripped.

    If the user hits EOF (Unix: Ctl-D, Windows: Ctl-Z+Return), raise EOFError.

    On Unix, GNU readline is used if enabled.  The prompt string, if given,

    is printed without a trailing newline before reading.

input：读取用户输入值，返回字符串。

In [114]: input()
123
Out[114]: '123'

In [115]: input()
哈哈哈哈哈
Out[115]: '哈哈哈哈哈'

In [116]: input("Please Enter text:")
Please Enter text:hello world!
Out[116]: 'hello world!'

9.callable

>>> help(callable)

Help on built-in function callable in module builtins:

callable(...)

    callable(object) -> bool

    

    Return whether the object is callable (i.e., some kind of function).

    Note that classes are callable, as are instances of classes with a

    __call__() method.

判断某对象是否可被调用

In [1]: callable(abs)
Out[1]: True

In [2]: callable(map)
Out[2]: True

In [3]: def sayhello():
...:     print ("hello")
...:

In [4]: callable(sayhello)
Out[4]: True

In [5]: callable('abc')
Out[5]: False

In [6]: callable(5)
Out[6]: False

In [7]: class A:
...:     def __init__(self,value):
...:         self.value = value
...:

In [8]: callable(A)
Out[8]: True

10.删除对象的某个属性

help(delattr)

Help on built-in function delattr in module builtins:

delattr(...)

    delattr(object, name)

    

    Delete a named attribute on an object; delattr(x, 'y') is equivalent to

    ``del x.y''.

In [19]: class A:
...:     def __init__(self,value):
...:         self.value = value
...:

In [20]: a = A('5')

In [21]: a.value
Out[21]: '5'

In [22]: delattr(a,'value')

In [23]: a.value   #属性已删除，所以报错。
---------------------------------------------------------------------------
AttributeError                            Traceback (most recent call last)
<ipython-input-23-669656c3105a> in <module>()
----> 1 a.value

AttributeError: 'A' object has no attribute 'value'

11.enumerate

>>> help(enumerate)

Help on class enumerate in module builtins:

class enumerate(object)

 |  enumerate(iterable[, start]) -> iterator for index, value of iterable

 |  

 |  Return an enumerate object.  iterable must be another object that supports

 |  iteration.  The enumerate object yields pairs containing a count (from

 |  start, which defaults to zero) and a value yielded by the iterable argument.

 |  enumerate is useful for obtaining an indexed list:

 |      (0, seq[0]), (1, seq[1]), (2, seq[2]), ...

 |  

 |  Methods defined here:

 |  

 |  __getattribute__(self, name, /)

 |      Return getattr(self, name).

 |  

 |  __iter__(self, /)

 |      Implement iter(self).

 |  

 |  __new__(*args, **kwargs) from builtins.type

 |      Create and return a new object.  See help(type) for accurate signature.

 |  

 |  __next__(self, /)

 |      Implement next(self).

 |  

 |  __reduce__(...)

 |      Return state information for pickling.

根据可迭代对象创建枚举对象

In [1]: L = [1,2,3,4,5,6,7,8,9]

In [2]: for index,value in enumerate(L):
...:     print (index,value)
...:
0 1
1 2
2 3
3 4
4 5
5 6
6 7
7 8
8 9

In [3]: for index,value in enumerate(L,start = 5):   #也可以指定起始索引
...:     print (index,value)
...:
5 1
6 2
7 3
8 4
9 5
10 6
11 7
12 8
13 9

12.eval

>>> help(eval)

Help on built-in function eval in module builtins:

eval(...)

    eval(source[, globals[, locals]]) -> value

    

    Evaluate the source in the context of globals and locals.

    The source may be a string representing a Python expression

    or a code object as returned by compile().

    The globals must be a dictionary and locals can be any mapping,

    defaulting to the current globals and locals.

    If only globals is given, locals defaults to it.

表达式求值。

In [7]: eval('1+2*6')

Out[7]: 13

In [8]: eval('abs(-5)')

Out[8]: 5

13.exec

>>> help(exec)

Help on built-in function exec in module builtins:

exec(...)

    exec(object[, globals[, locals]])

    

    Read and execute code from an object, which can be a string or a code

    object.

    The globals and locals are dictionaries, defaulting to the current

    globals and locals.  If only globals is given, locals defaults to it.

执行动态语句块

In [12]: exec('a = 1 + 1')

In [13]: a
Out[13]: 2

14.zip

>>> help(zip)

Help on class zip in module builtins:

class zip(object)

 |  zip(iter1 [,iter2 [...]]) --> zip object

 |  

 |  Return a zip object whose .__next__() method returns a tuple where

 |  the i-th element comes from the i-th iterable argument.  The .__next__()

 |  method continues until the shortest iterable in the argument sequence

 |  is exhausted and then it raises StopIteration.

 |  

 |  Methods defined here:

 |  

 |  __getattribute__(self, name, /)

 |      Return getattr(self, name).

 |  

 |  __iter__(self, /)

 |      Implement iter(self).

 |  

 |  __new__(*args, **kwargs) from builtins.type

 |      Create and return a new object.  See help(type) for accurate signature.

 |  

 |  __next__(self, /)

 |      Implement next(self).

 |  

 |  __reduce__(...)

 |      Return state information for pickling.

聚合传入的每个迭代器中相同位置的元素，返回一个新的元组类型迭代器

In [14]: a = [1,2,3,4,5]

In [15]: b = ['a','b','c','d','e','f']

In [16]: for i in zip(a,b):
...:     print (i)
...:
(1, 'a')
(2, 'b')
(3, 'c')
(4, 'd')
(5, 'e')