Permutations in python

Question

I have a list of sets and I want to get a list of all sublists possible. This is what I ve written until now. For some reason it is not including the last position and I don't understand why.

def all_sublists(sets):
 l = []
 for i in range(0,len(sets)):
 for j in range(0,len(sets)):
 for step in range(1,len(sets)):
 if sets[i:j:step] not in l:
 l.append(sets[i:j:step]) 
 return l
def fun(sets):
 x = all_sublists(sets)
 for element in x:
 print(element)
 return 0

And this is my output: enter image description here

• JacobIRR: This may be helpful (the source code for the python itertools module) : github.com/python/cpython/blob/master/Modules/itertoolsmodule.c
• sonus21: for j in range(0,len(sets)+1): for step in range(1,len(sets)): if sets[i:j:step] not in l: l.append(sets[i:j:step])
• Diogo Silva: @JacobIRR my teacher doesn t want us to use itertools for some reason
• Diogo Silva: @sonus21 I want to know why it doesn t work this way, I think it makes sense like this
• 10 Rep: @DiogoSilva The reason this won't work is because the larger the list, the more time it will take. This has exponential time.

Answer 1

Use the itertools library.

import itertools as it
my_list = [{1,2,3},{2,4},{3,4},{4,5}]
combinations = it.chain(*(it.combinations(my_list,i) for i in range(len(my_list))))
print(list(combinations))

EDIT:

Well, powersets are 2^N given a list of size N, hence your formula needs to account for the binary selection process. Something like

def powerset(sets):
 pset = []
 for i in range(2**len(sets)):
 subset = []
 for n,keep in enumerate(bin(i)[2:].zfill(len(sets))):
 if keep == '1':
 subset.append(sets[n])
 pset.append(subset)
 return pset
pset([1,2,3])

Answer 2

From https://docs.python.org/3/library/itertools.html#itertools-recipes:

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))

Answer 3

Add +1 in second loop. range(0,len(sets)+1)

def all_sublists(sets):
 l = []
 for i in range(0,len(sets)):
 for j in range(0,len(sets)+1):
 for step in range(1,len(sets)):
 if sets[i:j:step] not in l:
 l.append(sets[i:j:step]) 
 return l
def fun(sets):
 x = all_sublists(sets)
 for element in x:
 print(element)
 return 0