How do for loops in lists work in Python?

Question

Sometimes when I look at other posts in stack overflow I see this:

my_list = [x.split(",") for x in my_list]

How does the for loop work in lists? Where can I find the documentation for this?

(I tried looking it up on the docs but I can't find it)

Its called a list comprehension: https://www.w3schools.com/python/python_lists_comprehension.asp — Rohith Nambiar, Mar 19 '22 at 02:50
The [python docs](https://docs.python.org/3/tutorial/datastructures.html#list-comprehensions) — Mark, Mar 19 '22 at 02:59

score 1 · Accepted Answer · edited Mar 22 '22 at 04:41

It's called List Comprehensions and it is basically a quick way to build a sequence. The code you demonstrate basically means,

for each x in my_list, perform x.split(","), and then put all the result in a new list, which is then passed to my_list.

It is equivalent to:

new_list = []

for x in my_list:
    y = x.split(",")
    new_list.append(y)

my_list = new_list

So you can see with list comprehensions it is a lot simpler.

1 Answers1