I want itertools to return a list of lists

Question

I'm using itertools to generate all possible permutations of a list. I would like it to return a list of lists, but this is not what I'm getting.

For example

import itertools
print list(itertools.permutations([1, 2]))

returns

>>> [(1, 2), (2, 1)]

But I was expecting

>>> [[1, 2], [2, 1]]

Is it possible?

Answer 1

Just map your tuples to lists:

import itertools
try:
    # Python 2, use Python 3 iterator version of map
    from future_builtins import map
except ImportError:
    # already using Python 3
    pass

map(list, itertools.permutations([1, 2]))

In Python 3, map() is an iterator too, so the tuples are converted to lists as you iterate.

I'm assuming here that you don't need the full permutations result in one go. You can always call list() on the map(), or use a list comprehension instead if you do:

[list(t) for t in itertools.permutations([1, 2])]

or for Python 2, just drop the from future_builtins import and leave map to produce a list.

Answer 2

You can use a list comprehension to convert each tuple to a list and collect the results in a list:

>>> [list(p) for p in itertools.permutations([1, 2])]
[[1, 2], [2, 1]]