Fix Python – TypeError: a bytes-like object is required, not ‘str’ when writing to a file in Python 3

I’ve very recently migrated to Python 3.5.
This code was working properly in Python 2.7:
with open(fname, ‘rb’) as f:
lines = [x.strip() for x in f.readlines()]

for line in lines:
tmp = line.strip().lower()
if ‘some-pattern’ in tmp: continue
# … code

After upgrading to 3.5, I’m getting the:

TypeError: a bytes-like object is re….