Question

I have a list. It contains x lists, each with y elements.
I want to pair each element with all the other elements, just once, (a,b = b,a)

EDIT: this has been criticized as being too vague.So I’ll describe the history.
My function produces random equations and using genetic techniques, mutates and crossbreeds them, selecting for fitness.
After a number of iterations, it returns a list of 12 objects, sorted by fitness of their ‘equation’ attribute.
Using the ‘parallel python’ module to run this function 8 times, a list containing 8 lists of 12 objects (each with an equation attribute) each is returned.
Now, within each list, the 12 objects have already been cross-bread with each other.
I want to cross-breed each object in a list with all the other objects in all the other lists, but not with the objects within it’s own list with which it has already been cross-bread. (whew!)

Answer 1

itertools.product is your friend.

about removing the duplicates, try with a set of sets.

Now it’s a little bit clearer what you want:

import itertools

def recombinate(families):
    "families is the list of 8 elements, each one with 12 individuals"
    for fi, fj in itertools.combinations(families, 2):
        for pair in itertools.product(fi, fj):
            yield pair

basically, take all the 2-combinations of families (of those produced in parallel) and for each pair of families, yield all the pairs of elements.