[英]Why am I getting this IndexError
a = [1,2,1,5]
b = [1,1,5]
c = [a[index] for index in b]
print(c)
and I got this error:我得到了这个错误:
IndexError
Traceback (most recent call last)
<ipython-input-158-e03093b57c86> in <module>
2 b=[1,1,5]
3 index=0
----> 4 c=[a[index] for index in b]
5 c
<ipython-input-158-e03093b57c86> in <listcomp>(.0)
2 b=[1,1,5]
3 index=0
----> 4 c=[a[index] for index in b]
5 c
IndexError: list index out of range
I believe you wanted to do this: (Slight modification of your code)我相信您想这样做:(对您的代码稍作修改)
c = [a[index] for index in range(len(b))]
This iterates over the length of list b, which is [0, 1, 2] as len(b) = 3. And these are valid indexes for list a.这会迭代列表 b 的长度,即 [0, 1, 2] 为 len(b) = 3。这些是列表 a 的有效索引。
In the above implemenation, the list you are iterating over is [1, 1, 5].在上述实现中,您正在迭代的列表是 [1, 1, 5]。 And a[5] does not exist since list a has only 4 elements.
并且 a[5] 不存在,因为列表 a 只有 4 个元素。
Hope this helps!希望这可以帮助!
The reason you are getting this is error is because your list b
has got the number 5
and your list a
is of length 5 and hence has a maximum index of 4, since indexing starts from 0.你得到这个错误的原因是你的列表
b
有数字5
并且你的列表a
的长度为 5,因此最大索引为 4,因为索引从 0 开始。
So when you try and grab the value from list a
at index 5
, there is no such value which results in the error: list index out of range
因此,当您尝试从索引
5
处的列表a
中获取值时,没有这样的值会导致错误: list index out of range
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