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')