How to iterate over the first n elements of a list?

问题

Say I've got a list and I want to iterate over the first n of them. What's the best way to write this in Python?

回答1:

The normal way would be slicing:

for item in your_list[:n]: 
    ...

回答2:

I'd probably use itertools.islice (<- follow the link for the docs), which has the benefit of working with any iterable object.

回答3:

You can just slice the list:

>>> l = [1, 2, 3, 4, 5]
>>> n = 3
>>> l[:n]
[1, 2, 3]

and then iterate on the slice as with any iterable.

回答4:

Python lists are O(1) random access, so just:

for i in xrange(n):
    print list[i]

来源：https://stackoverflow.com/questions/2688079/how-to-iterate-over-the-first-n-elements-of-a-list