# All possibilities to split a list into two lists

I have a list with some elements and want to iterate over all possible ways to divide this list into two lists. By that I mean all combinations, so the order doesn’t matter (i.e. Element 1 and 3 could be in the one list and Element 2 in the other). Currently I do it like this, where `facs` is my initial list:

```patterns = []
for i in range(2**(len(facs)-1)):
pattern = []
for j in range((len(facs)-1)):
pattern.append(i//(2**j)%2)
patterns.append(pattern)

for pattern in patterns:
l1 = [facs[-1]]
l2 = []
for i in range(len(pattern)):
if pattern[i] == 1:
l1.append(facs[i])
else:
l2.append(facs[i])
```

So I basically create a list of length `2^(len(facs)-1)` and fill it with every possible combination of ones and zeros. I then ‘overlay’ every pattern with `facs`, except for the last element of `facs` which is always in `l1`, as I’d otherwise get every result twice, as I handle two lists the same, no matter what lists is `l1` or `l2`.

Is there a faster and more elegant (shorter/more pythonic) way to do this?

`itertools` has `product()` which could be used to generate the masks and `izip()` which could combine the lists for easy filtering. As a bonus, since they return iterators, they don’t use much memory.
```from itertools import *