Pythonic way of iterating over ordered collections

Last Updated: November 18, 2023 8:00 PM UTC

Last edited by:

Steele Farnsworth <[email protected]>

Rewriting of non-code sections.

The previous version began with "Iterating over range-len is a common approach ...", which sounds like an endorsement. Also removed "is guaranteed to produce elements in the same order", as I don't think anyone is actually confused about that. (I wrote the previous version--this is a criticism of my own writing.)

Beginners often iterate over range(len(...)) because they look like Java or C-style loops, but this is almost always a bad practice in Python.

for i in range(len(my_list)):
    do_something(my_list[i])

It's much simpler to iterate over the list (or other sequence) directly:

for item in my_list:
    do_something(item)

Python has other solutions for cases when the index itself might be needed. To get the element at the same index from two or more lists, use zip. To get both the index and the element at that index, use enumerate.