枚举对象上的 python dict 函数

发布于 2024-08-29 22:43:56 字数 87 浏览 8 评论 0原文

如果我有一个枚举对象 x，为什么要执行以下操作：

dict(x)

清除枚举序列中的所有项目？

原文

If I have an enumerate object x, why does doing the following:

dict(x)

clear all the items in the enumerate sequence?

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爱你是孤单的心事 2024-09-05 22:43:56

enumerate 创建一个迭代器。迭代器是一个Python对象，它只知道序列的当前项以及如何获取下一个，但无法重新启动它。因此，一旦您在循环中使用了迭代器，它就无法再为您提供任何项目，并且看起来是空的。

如果你想从迭代器创建一个真实的序列，你可以对其调用list。

stuff = range(5,0,-1)
it = enumerate(stuff)
print dict(it), dict(it) # first consumes all items, so there are none left for the 2nd call

seq = list(enumerate(stuff)) # creates a list of all the items
print dict(seq), dict(seq) # you can use it as often as you want

enumerate creates an iterator. A iterator is a python object that only knows about the current item of a sequence and how to get the next, but there is no way to restart it. Therefore, once you have used a iterator in a loop, it cannot give you any more items and appears to be empty.

If you want to create a real sequence from a iterator you can call list on it.

stuff = range(5,0,-1)
it = enumerate(stuff)
print dict(it), dict(it) # first consumes all items, so there are none left for the 2nd call

seq = list(enumerate(stuff)) # creates a list of all the items
print dict(seq), dict(seq) # you can use it as often as you want

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