Python内置函数enumerate()

Posted 2020-09-23

enumerate()是Python的内置函数。

 1 help(enumerate)
 2 Help on class enumerate in module builtins:
 3 class enumerate(object)
 4   enumerate(iterable[, start]) -> iterator for index, value of iterable
 5   #enumerate(可迭代变量[,开始下标])->返回迭代变量的索引和值。  （注意，字典和集合也能使用，取位置作为索引）
 6   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.
 7 enumerate is useful for obtaining an indexed list: 
 8       (0, seq[0]), (1, seq[1]), (2, seq[2]), ...
 9  
10  Methods defined here:
11   
12 __getattribute__(self, name, /)
13       Return getattr(self, name).
14   
15 __iter__(self, /)
16       Implement iter(self).
17   
18 __new__(*args, **kwargs) from builtins.type
19      Create and return a new object.  See help(type) for accurate signature.
20 
21 __next__(self, /)
22      Implement next(self).
23  
24 __reduce__(...)
25     Return state information for pickling.

对于一个可迭代的iterable/可遍历的对象（如列表，字符串，元组，字典和集合）。

enumerate()多用于在for循环中得到计数；enumerate()返回的是一个enumerate对象。

 1 for i in enumerate([1,2,3,4,5]):  #对列表作用
 2     print(i)
 3     
 4 (0, 1)
 5 (1, 2)
 6 (2, 3)
 7 (3, 4)
 8 (4, 5)
 9 
10 for i in enumerate((1,2,3)): #对元组作用
11     print(i)
12     
13 (0, 1)
14 (1, 2)
15 (2, 3)
16 
17 for i in enumerate(‘help‘): #对字符串作用
18     print(i)
19     
20 (0, ‘h‘)
21 (1, ‘e‘)
22 (2, ‘l‘)
23 (3, ‘p‘)
24 
25 for i in enumerate({‘name‘:‘zoe‘,‘age‘:18}):  #对字典作用
26     print(i)
27     
28 (0, ‘name‘)
29 (1, ‘age‘)
30 
31 for i in enumerate({12,3}): #对元组作用
32     print(i)
33     
34 (0, 3)
35 (1, 12)