python常用内置函数1

Posted 2020-10-27 ghostwu

1，abs 求绝对值

>>> abs( -1 )
1
>>> abs( 1 )
1
>>> 

2，max, min求序列最大值与最小值

>>> l = [ 1, 10, -6, 2, 100 ]
>>> max( l )
100
>>> min( l )
-6

3，len求列表的长度

>>> s = ‘ghostwu‘
>>> len( s )
7
>>> l = [ 10, 20, 30 ]
>>> len( l )
3
>>> t = ( 10, 20 )
>>> len( t )
2
>>> dic = { ‘a‘ : 10, ‘b‘ : 20, ‘c‘ : -1, ‘d‘ : 100 }
>>> len( dic )
4

4，divmod求商和余数

>>> divmod( 1, 2 )
(0, 1)
>>> divmod( 2, 1 )
(2, 0)
>>> 

5，pow，两个值，幂运算，3个值，先幂运算，再除以第三个值，求余数

>>> pow( 3, 4 )
81

>>> pow( 2, 2, 6 )
4
>>> 

6，callable测试函数是否可以被调用

>>> callable( min )
True
>>> callable( f )
Traceback (most recent call last):
  File "<stdin>", line 1, in <module>
NameError: name ‘f‘ is not defined
>>> callable( abs )
True
>>> def f():
...     pass
... 
>>> callable( f )
True

7，类型判断

>>> l = [ 10, 20 ]
>>> type( l )
<type ‘list‘>
>>> type( [] )
<type ‘list‘>
>>> if( type( [] ) == type( l ) ):
...     print ‘yes‘
... 
yes
>>> t = ( 10, 20 )
>>> if( type( [] ) == type ( t ) ):
...     print ‘yes‘
... else:
...     print ‘no‘
... 
no
>>> 

也可以用isinstance判断 

>>> l = [ 10, 20 ]
>>> isinstance( l, list )
True
>>> type( () )
<type ‘tuple‘>
>>> isinstance( ( 10, 20 ), tuple )
True
>>> isinstance( l, tuple )
False
>>> 

8，cmp比较字符串大小

>>> cmp( ‘a‘, ‘b‘ )
-1
>>> cmp( ‘b‘, ‘ac‘ )
1
>>> cmp( ‘a‘, ‘ab‘ )
-1
>>> cmp( ‘a‘, ‘a‘ )
0
>>> 

9，range与类型转换等

>>> range( 1, 10 )
[1, 2, 3, 4, 5, 6, 7, 8, 9]
>>> range( -1, -10, -1 )
[-1, -2, -3, -4, -5, -6, -7, -8, -9]
>>> range( 1, 10, 5 )
[1, 6]
>>> 

>>> s = ‘ghostwu‘
>>> type( s )
<type ‘str‘>
>>> int( s )
Traceback (most recent call last):
  File "<stdin>", line 1, in <module>
ValueError: invalid literal for int() with base 10: ‘ghostwu‘
>>> s = ‘20‘
>>> type( s )
<type ‘str‘>
>>> int( s )
20
>>> type( s )
<type ‘str‘>
>>> s + ‘abc‘
‘20abc‘
>>> int( s ) + ‘abc‘
Traceback (most recent call last):
  File "<stdin>", line 1, in <module>
TypeError: unsupported operand type(s) for +: ‘int‘ and ‘str‘
>>> int( s ) + 10
30
>>> 

字符串为数值类型的才能转成整形

当然还有其他类型转换等