为什么不能"i"在for循环中被操纵 [英] Why can't "i" be manipulated inside for-loop

问题描述

为什么这样做:

for i in range(10):
 i += 1
 print(i)

返回:

1
2
3
4
5
6
7
8
9
10

代替:

2
4
6
8
10

?

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推荐答案

for i in range(10):
    i += 1
    print(i)

等同于

iterator = iter(range(10))
try:
    while True:
        i = next(iterator)
        i += 1
        print(i)
except StopIteration:
    pass

iter(range(10))产生的iterator将在每次调用next时产生值0，1，2 ... 8和9，然后提高在第11个电话上.

The iterator that iter(range(10)) produces will yield values 0, 1, 2... 8 and 9 each time next is called with it, then raise StopIteration on the 11th call.

因此，您可以看到i在每次迭代中都被range(10)中的新值覆盖，并且没有增加，例如C风格的for循环.

Thus, you can see that i gets overwritten in each iteration with a new value from the range(10), and not incremented as one would see in e.g. C-style for loop.

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