My Loop for printing text file goes to infinity

[snippsat]

How would it print forever? If f has come to a line which is empty wouldnt it stop?

No it would not stop,it always read whole file to the end using while or for loop.
A better way,so can iterate over file object line bye line(do not need readline()).

with open('cities.txt') as f:
    for line in f:
        print(line.strip())

Example how stop(break out of loop) if there is a empty line.

with open('cities.txt') as f:
    for line in f:
        if line in ('', '\n'):
            break
        print(line.strip())