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In [1]: l = [1,2,3] In [2]: s = 'abcdef' In [3]: for x in l:print(x) 1 2 3 In [4]: for x in s:print(x) a b c d e f # 能for 循环输出 说明是可迭代对象 In [5]: iter? Docstring: iter(callable, sentinel) -> iterator Get an iterator from an object. In the first form, the argument must supply its own iterator, or be a sequence. In the second form, the callable is called until it returns the sentinel. Type: builtin_function_or_method # iter 可以从可迭代对象 --> 迭代器对象 In [6]: iter(l) Out[6]: <list_iterator at 0x111aa44e0> In [11]: l.__iter__() #等价于 iter(l) Out[11]: <list_iterator at 0x111ad9940> In [7]: iter(s) Out[7]: <str_iterator at 0x111aae358> In [12]: s.__iter__() # 等价于 iter(s) Out[12]: <str_iterator at 0x111b084a8> |
总结: iter先去找 iter 如果没有就去找 getitem
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In [16]: ll = iter(l) In [17]: ll Out[17]: <list_iterator at 0x111b508d0> In [19]: ll.__next__() Out[19]: 1 In [20]: ll.__next__() Out[20]: 2 In [21]: ll.__next__() Out[21]: 3 In [22]: ll.__next__() --------------------------------------------------------------------------- StopIteration Traceback (most recent call last) ----> 1 ll.__next__() StopIteration: |
for 循环就是一直调用这个next的方法,当遇到StopIteration循环停止.
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