stocking_allocator.py

import random

peeps = {
        'Matt': '',
        'Al': '',
        'Bebop': '',
        'Mum': '',
        'Dad': '',
        'Gramps': ''
    }


# Generate all permutations

def all_perms(elements):
    if len(elements) <=1:
        yield elements
    else:
        for perm in all_perms(elements[1:]):
            for i in range(len(elements)):
                # nb elements[0:1] works in both string and list contexts
                yield perm[:i] + elements[0:1] + perm[i:]

ns = list(peeps.keys())
names = list(range(1,len(peeps)+1))

possible = list(all_perms(names))


# Take out any non-derangements
possible2 = filter(lambda perm: not any([i for i, j in zip(perm, names) if i == j]), possible)


# Take out any cycles
possible3 = filter(lambda perm: not any(i for i in perm if perm[perm[i-1]-1] == i), possible2)


# Take out any combinations where Grampa isn't buying for Mum
gramps = ns.index('Gramps')+1
mum = ns.index('Mum')+1
possible4 = filter(lambda perm: perm[gramps-1] == mum, possible3)



# Select one of them at random
choice = random.choice(list(possible4))

final_list = [ns[i-1] for i in choice]

for i, j in zip(ns, final_list):
    print('{} = {}'.format(i, j))