How to loop through a list in Python two items at a time?

Community Feedback
,
1

How can I loop through a list in Python and process two list items at a time?

I want to loop through a Python list, similar to this logic in another language:

for(int i = 0; i < list.length(); i+=2)
{
   // do something with list[i] and list[i + 1]
}

What’s the best way to accomplish this using a for loop increment by 2 in Python?

2

Alright, I’ve worked with this quite a bit. One simple way to loop through a list in Python two items at a time is by using a for loop increment by 2 python. Here’s how you can do it with the range function in Python:

Python 2:

for i in xrange(0, 10, 2):
    print(i)

Python 3:

for i in range(0, 10, 2):
    print(i)

Note: In Python 2, xrange is more memory-efficient than range because it generates an iterable, whereas range creates a list. So, keep that in mind if you’re working with Python 2.

3

Good point, @tim-khorev! Building on that, you can loop through pairs of elements at a time using zip and slicing. It’s a neat trick that I use often with lists. Here’s an example:

my_list = [1, 2, 3, 4, 5, 6]
for x, y in zip(my_list[::2], my_list[1::2]):
    print(x, y)

This way, you’re able to process the list in pairs without manually managing the index. It’s pretty useful when you want to group adjacent items together. Still, the for loop increment by 2 python approach works great too depending on the situation!

6

Exactly, @mark-mazay! I like both methods you mentioned. One more alternative I find handy is using enumerate with a manual increment. This can be especially useful when you need more control over the indices, like checking for certain conditions. Here’s how it looks:

my_list = [1, 2, 3, 4, 5, 6]
for i, value in enumerate(my_list):
    if i % 2 == 0:
        print(value, my_list[i+1] if i+1 < len(my_list) else None)

The key thing here is to check if the index is even (i % 2 == 0) and then access the next item in the list. With this approach, you can also manage edge cases more easily. This too is a solid example of for loop increment by 2 python in action, but with a bit more flexibility.