Question

How to read n lines from a file instead of just one when iterating over it? I have a file which has well defined structure and I would like to do something like this:

for line1, line2, line3 in file:
    do_something(line1)
    do_something_different(line2)
    do_something_else(line3)

but it doesn’t work:

ValueError: too many values to unpack

For now I am doing this:

for line in file:
    do_someting(line)
    newline = file.readline()
    do_something_else(newline)
    newline = file.readline()
    do_something_different(newline)
... etc.

which sucks because I am writing endless ‘newline = file.readline()‘ which are cluttering the code.
Is there any smart way to do this ? (I really want to avoid reading whole file at once because it is huge)

Answer 1

Basically, your fileis an iterator which yields your file one line at a time. This turns your problem into how do you yield several items at a time from an iterator. A solution to that is given in this question. Note that the function isliceis in the itertools module so you will have to import it from there.