Recursively generate combinations with Python

Question

I am trying to provide a recursive method that provides a list of all the possible combinations when given a list of courses. E.g course = [Entree, Dessert] This is what I have so far:

Entree = ["pumkinsoup","antipasto"]
Dessert = ["cheesecake", "icecream", "tiramisu", "cheeseplatter"]
courses = [Entree, Dessert]

def make_orders(courses):
    dishes_so_far = []
    recursive_make_orders(dishes_so_far, courses)

def recursive_make_orders(dishes_so_far, courses):
    n = len(courses)
    if n==0 :
        print(dishes_so_far)
    else:
        current_courses = courses[0]

        for D in current_courses:
            dishes_so_far.append(D)
            recursive_make_orders(dishes_so_far , courses[1:len(courses)])

\I am trying to make it so that it prints out the combination like [[pumkinsoup,cheesecake],[punkinsoup, icecream]] and etc but its actually giving me [pumkinsoup, cheesecake, icecream] and so on.

Tried adding it with addition instead of append and it gave me an error.

This is homework, so a recursive method is required.

Please be more detailed in what you want to accomplish. Example output is fine, but not enough. And don't post your attempt to solve it here. It's distracting and not fun to dissect it. I think this explains downvotes. — ash
– ash, Commented Sep 17, 2013 at 10:26
@ash actually I disagree - while some may find it distracting, a genuine attempt to solve the problem is more than welcome and is in fact encouraged by the community. No one likes "gimme teh codez" questions... — Jon Clements
– Jon Clements, Commented Sep 17, 2013 at 10:28
@ash: What? I thought mattgemmell.com/2008/12/08/what-have-you-tried was the approach here on SO? — Niclas Nilsson
– Niclas Nilsson, Commented Sep 17, 2013 at 10:29
After the line dishes_so_far.append(D) , print courses, current_courses, dishes_so_far to see their contents before you call recursive_make_orders(dishes_so_far , courses[1:len(courses)]) — Mp0int
– Mp0int, Commented Sep 17, 2013 at 10:51

Jon Clements · Accepted Answer · 2013-09-17 10:22:43Z

2

You're not too far off - use itertools.product and *courses to unpack to it:

from itertools import product

for course in product(*courses):
  print course

('pumkinsoup', 'cheesecake')
('pumkinsoup', 'icecream')
('pumkinsoup', 'tiramisu')
('pumkinsoup', 'cheeseplatter')
('antipasto', 'cheesecake')
('antipasto', 'icecream')
('antipasto', 'tiramisu')
('antipasto', 'cheeseplatter')

answered Sep 17, 2013 at 10:22

Jon Clements

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3 Comments

user2784327 Over a year ago

sorry i should have stated that recursive method needs to be used, according to the question i have been given

zero323 Over a year ago

@JonClements List comprehension would be probably more pythonic ;)[[entree, desert] for entree in Entree for desert in Dessert]

zero323 Over a year ago

@JonClements True, although if I remember correctly, itertools have problems of it's own.

roman · Accepted Answer · 2013-09-17 10:56:56Z

1

If you want recursive version, you can do something like this:

def worker(entree, dessert):
    d = []
    if not entree or not dessert: return d

    d.append((entree[0], dessert[0]))
    d += worker(entree[1:], dessert)
    d += worker(entree, dessert[1:])
    return d

Your version is not working as you said because courses now a list of lists, and courses[0] is just Entree, so you recursively constructiong new list from Entree.

edited Sep 17, 2013 at 10:56

answered Sep 17, 2013 at 10:40

roman

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