Let's ignore pyc files
Refactoring to enable reuse

Seems like problem 4 will need to factorize
Xrange is more fit here

TIL, xrange doesn't generate the whole list, it uses a generator, so it
saves memory
Add problem4

This one is different. I have spent a lot of time on this one. I'm using
unittest to try each part. The current strategy is ugly, but I will get
around it, eventually.
A solution for problem #4

It sucks, 1.3s for the 3 digit answer…

Already know how to improve it a bit, for example by not computing all
the possible way before testing each of them.

Mixing ways_to_split_in_two_a_set and found_possible_combination is a
good first step
Reducing almost in half the time

Just by being more careful with assignments, appends, and concatenates.
Removing unnecessary deepcopy