I just simply want to remove all the elements in the python list one by one by remove() method, but find out that does not work. I run the code below:
a=[1,2,3]
for i in a:
a.remove(i)
print a
and it shows
[2]
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It's a common pitfallOhad Eytan– Ohad Eytan2016-08-20 21:40:28 +00:00Commented Aug 20, 2016 at 21:40
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1 Answer
What's happening there is that you are changing a list while you iterate over it, but the iterator on that list will not get updated with your changes. So as you delete the first element (index = 0) in the first iteration, the second one (index = 1) becomes now the first (index = 0), but the iterator will next return the second (index = 1) element instead of returning (again) the first one that has changed and has been skipped. Step by step:
Iterator starts at index 0, which is element
1. List is[1, 2, 3]. You remove that element and end up with[2, 3].Iterator moves to index 1, which is element
3(note 2 has been skipped). You remove that element and end up with[2].Iterator moves to index 2, which doesn't exist, so iteration is over.
