Question

This is part of my program for generating punnet squares. It should separate a “genome” of the form [[‘A’,’a’],[‘b’,’b’],[‘C’,C’]…] into possible gametes:

def gene_erator2(gen):
    gam = [[], []]
    q = 0
    for x in gen:
        q = q + 1
        if q > 1:
            gamgam = gam[:]
            for z in gam: 
                gamgam.append(z)
            gam = gamgam[:]
        for y in range(len(gam)):
            if y < len(gam)/2:
                gam[y].append(x[0])
            else:
                gam[y].append(x[1])
    return gam

When I execute

gene_erator2([['A','a'], ['B','b'], ['X','Y']])

I get

[['A', 'B', 'b', 'X', 'X', 'Y', 'Y'], ['a', 'B', 'b', 'X', 'X', 'Y', 'Y'], ['A', 'B', 'b', 'X', 'X', 'Y', 'Y'], ['a', 'B', 'b', 'X', 'X', 'Y', 'Y'], ['A', 'B', 'b', 'X', 'X', 'Y', 'Y'], ['a', 'B', 'b', 'X', 'X', 'Y', 'Y'], ['A', 'B', 'b', 'X', 'X', 'Y', 'Y'], ['a', 'B', 'b', 'X', 'X', 'Y', 'Y']]

instead of the expected

[['A', 'B', 'X'], ['a', 'B', 'X'], ['A', 'b', 'X'], ['a', 'b', 'X], ['A', 'B', 'Y'], ['a', 'B', 'Y'], ['A', 'b', 'Y'], ['a', 'b', 'Y']]

….What? I mean, just What?

EDIT:
I now know the function that does what I want thanks to Shang, but I still want to know what was wrong with my code….

Answer 1

There’s a function that does what you want in the standard library.

import itertools

def gene_erator2(gen):
    return itertools.product(*gen)

This returns an iterator, which lets you iterate over all the combinations.

>>> i = gene_erator2([['A','a'],['B','b'],['X','Y']])
>>> list(i)
[('A', 'B', 'X'), ('A', 'B', 'Y'), ('A', 'b', 'X'), ('A', 'b', 'Y'), ('a', 'B', 'X'), ('a', 'B', 'Y'), ('a', 'b', 'X'), ('a', 'b', 'Y')]