TIL: How to use list comprehensions in python

In the past, if I wanted to make a new list by pulling values out of an existing list based on a condition I would have done something like:

def listItems():
    a = [1, 4, 9, 16, 25, 36, 49, 64, 81, 100]
    new = []
    for num in a:
        if num % 2 != 0:
            new.append(num)
    print new

But, I figured out via https://docs.python.org/3/tutorial/datastructures.html#list-comprehensions that list comprehenisions can dramatically compress these functions while still maintaining readability. Here’s an example of a list comprehension that would render the same output as the expanded function above:

def listComp():
    a = [1, 4, 9, 16, 25, 36, 49, 64, 81, 100]
    new = [ num for num in a if num % 2 != 0] 
    print new

Boom!

The syntax is a little weird because python has so little structure to it “num for num in a…”, but makes more sense if you’re referencing a tuple, where it would be “( 1, 2 ) for num in a…”