making it more efficient

[MahyarFardin]

Reading file inside for loop is something costly!!!!

[dabeaz]

Deviates significantly from other course material. Would only accept if noted as some kind of comment attached to the original solution.

[dg1223]

with open(filename) is fine. It is computationally efficient. Explained here.

When we write:

with open(filename) as f:
    for line in f:
        # use line in code

the loop looks at one line at a time. This has the advantage of requiring very little memory — only enough memory to hold the chars of a single line at a time, even though the file might have thousands or millions of lines of text in total.

The suggested fix with f = open(filename, 'rt') needs to close the file with f.close() which is not included in the PR.