Nested for loops in list comprehension

Question

I'm new to python and just trying to learn how to make my code more pythonic. I'm reading a file into a list of strings and then reading these strings into their own list in python. This is my code.

data = [line.strip() for line in open(filename, 'r')]
data = [list(item) for item in data]

How can I do this in one line using nested for loops.

Answer 1

The for clauses go in the same order as if you had written a nested loop.

data = [list(item) for line in open(filename, 'r') for item in line.strip()]

You should be using a with statement, though:

with open(filename, 'r') as f:
    data = [list(item) for line in f for item in line.strip()]