找到列表中的变量时，Python 从列表中返回列表

Question

I'm a Python beginner. I'm trying to return a list from a list of lists into a new list of lists. I've looked extensively at similar questions, but cannot find the answer.

l1 = [['a','b','c','d'],['b','c','d','f'],['b','c','a','f']]

I would like to loop over l1 to check if 'a' is in a list, and when true then add that list to a new list of lists l2. I got this far (not very far):

l2 = []
for selector in l1:
    if 'a' in selector:
        l2.append(*#I don't know this part*)

What i would like is this result:

l2 = [['a','b','c','d'],['b','c','a','f']]

Any help would be much appreciated.

Answer 1

You can use a list comprehension to iterate over the inner lists

>>> [sub for sub in l1 if 'a' in sub]
[['a', 'b', 'c', 'd'], ['b', 'c', 'a', 'f']]

To complete the snippet of code you showed above, the way you'd use a for loop is

l2 = []
for selector in l1:
    if 'a' in selector:
        l2.append(selector)

>>> l2
[['a', 'b', 'c', 'd'], ['b', 'c', 'a', 'f']]