I’ve recently discovered list comprehensions in Python, and, boy, does this make me excited. Given my background in math, this is like finding a postcard from the past in my desk drawer, because they resemble set builder notation from set theory!

In Python, a list comprehension is another way of iterating through something and building a list. You could go with for loop:

L = []
for x in range(10):
    if x% 2 == 1:
        L.append(x**2)

Or you could do the same with a list comprehension:

L = [x**2 for x in range(10) if x% 2 == 1]

Isn’t it much neater? Some say that they are faster than for loops because, I qoute, “technically, they “run in a C speed”, while “the for loop runs in the python virtual machine speed”. However, as with anything, turns out it depends and one needs to timit in each particular case.
In any case, I find that it’s a beautiful construct, and if it speeds things up - that’s a good reason to learn to use them. It’s not too hard to transform a for loop into a list comprehension either. Here’s how you generally do it. This is your loop:

new_list = []
for i in what_you_are_iterating_through:
    if condition_based_on_i:
        new_list.append(what_you_add_to_new_list)

This is a list comprehension you can transform it to:

new_list = [what_you_add_to_new_list for i in what_you_are_iterating_through if condition_based_on_i]

If it gets too long, you can add line breaks for the sake of better readability:

new_list = [
	what_you_add_to_new_list 
	for i in what_you_are_iterating through
	if condition_based_on_i
]

A shorter construct, readable, and typically faster. What’s not to like?

As a side note, I was surprised to see that there’s no such intention action/refactoring in PyCharm. Perhaps, I’m missing something, but it seems like a doable IDE action. I’ve found a feature request for this and voted it up. If anyone else would like to see this implemented - feel free to add your vote as well here.