How to read a 8GB file in Python?

All you need to do is use the file object as an iterator.

for line in open("log.txt"):
    do_something_with(line)

Even better is using context manager in recent Python versions.

with open("log.txt") as fileobject:
    for line in fileobject:
        do_something_with(line)

This will automatically close the file as well.