You are using str
methods on an open file object.
You can read the file as a list of lines by simply calling list()
on the file object:
with open('goodlines.txt') as f:
mylist = list(f)
This does include the newline characters. You can strip those in a list comprehension:
with open('goodlines.txt') as f:
mylist = [line.rstrip('\n') for line in f]