Python学习笔记(三):常用内置函数学习

谁借莪１个温暖的怀抱￠ 2022-06-08 04:58 418阅读 0赞

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')