Question

Let’s say I have a file like this (pretend it were a matrix):

abcde
fghik
lmnop

I want to put this in a 2d list but with only columns up to index 3:

 #  0   1   2   3
 [['a','b','c','d'],
  ['f','g','h','i'],
  ['l','m','n','o']]

How does one do this using a list comprehension? I know I could loop, but I’m looking for a cleaner way.

f = open('file.txt')
lines = f.readlines()
matrix = [[a for a in b] for b in lines] # this gets all columns, up to 4

I could also use enumerate/if in the inner list comprehension to check for column. Is that the cleanest?

Answer 1

If I understand the question correctly, this should work (but perhaps I’m over simplifying). Note the [:4] in the inner comprehension:

f = open('file.txt')
lines = f.readlines()
matrix = [[a for a in b[:4]] for b in lines] # this gets all columns, up to 4