Question

I have a tuple of Action objects

I want to create a list of every possible permutation of the Action objects N deep.

i.e. if I have the actions Eat, Sleep, Drink, and N = 2

the list would be

[[Eat, Eat],
 [Eat, Sleep],
 [Eat, Drink],
 [Sleep, Eat],
 [Sleep, Sleep],
 [Sleep, Drink],
 [Drink, Eat],
 [Drink, Sleep],
 [Drink, Drink]]

Now, I have a much larger list than three Actions, and N will probably be 3 or more.

How would I do this in Python 2.7?

Answer 1

Sounds like you want the Cartesian product of a list with itself. Use itertools.product():

>>> import itertools, pprint
>>> mylist = ["Eat","Sleep","Drink"]
>>> my_combination = list(itertools.product(mylist, repeat = 2))
>>> pprint.pprint (my_combination)
[('Eat', 'Eat'),
 ('Eat', 'Sleep'),
 ('Eat', 'Drink'),
 ('Sleep', 'Eat'),
 ('Sleep', 'Sleep'),
 ('Sleep', 'Drink'),
 ('Drink', 'Eat'),
 ('Drink', 'Sleep'),
 ('Drink', 'Drink')]

The optional repeat argument controls how “deep” your list is.

Beware that the size of the list grows exponentially with the depth N. Don’t materialise the whole list at once – instead, use one element at a time.

# Don't do this - will crash Python with out-of-memory error
list(itertools.product(my_list, repeat = 100000))

# Iterate over the list instead
for one_combination in itertools.product(my_list, repeat = 100000):
    print (one_combination)