I'm trying to create a powerset in Python 3. I found a reference to the itertools
module, and I've used the powerset code provided on that page. The problem: the code returns a reference to an itertools.chain object, whereas I want access to the elements in the powerset. My question: how to accomplish this?
Many thanks in advance for your insights.
itertools functions return iterators, objects that produce results lazily, on demand.
You could either loop over the object with a for loop, or turn the result into a list by calling list() on it:
from itertools import chain, combinations
def powerset(iterable):
"powerset([1,2,3]) --> () (1,) (2,) (3,) (1,2) (1,3) (2,3) (1,2,3)"
s = list(iterable)
return chain.from_iterable(combinations(s, r) for r in range(len(s)+1))
for result in powerset([1, 2, 3]):
print(result)
results = list(powerset([1, 2, 3]))
print(results)
You can also store the object in a variable and use the next() function to get results from the iterator one by one.
Here's a solution using a generator:
from itertools import combinations
def all_combos(s):
n = len(s)
for r in range(1, n+1):
for combo in combinations(s, r):
yield combo
range should start at 0. And power sets should treat any duplicated input element as just occurring once. See github.com/jpgoldberg/powerset-generator for a package I'm developing based on your answer.Allen Downey's answer is what I would use, except I would replace the range with
range(n+1) since the empty set is considered an element of the power set.
This code can easily be rewritten as a one liner:
(combo for r in range(len(s) + 1) for combo in combinations(s, r))
Your choice whether to surround it with () for an iterator or [] for a list.
itertools?more_itertools.powerset(iterable)