Python how to read N number of lines at a time

Question

I am writing a code to take an enormous textfile (several GB) N lines at a time, process that batch, and move onto the next N lines until I have completed the entire file.

Answer 1

The question appears to presume that there is efficiency to be gained by reading an "enormous textfile" in blocks of N lines at a time. This adds an application layer of buffering over the already highly optimized stdio library, adds complexity, and probably buys you absolutely nothing.

Thus:

with open('my_very_large_text_file') as f:
    for line in f:
        process(line)

is probably superior to any alternative in time, space, complexity and readability.

See also Rob Pike's first two rules, Jackson's Two Rules, and PEP-20 The Zen of Python. If you really just wanted to play with islice you should have left out the large file stuff.