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

Say I've got a list and I want to itera开发者_开发问答te over the first n of them. What's the best way to write this in Python?

The normal way would be slicing:

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

I'd probably use itertools.islice (<- follow the link for the docs), which has the benefits of:

• working with any iterable object
• not copying the list

Usage:

import itertools

n = 2
mylist = [1, 2, 3, 4]
for item in itertools.islice(mylist, n):
    print(item)

outputs:

1
2

One downside is that if you wanted a non-zero start, it has to iterate up to that point one by one: https://stackoverflow.com/a/5131550/895245

Tested in Python 3.8.6.

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.

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

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