How to turn the result (in python) of itertools.permutations(“0123456789”) into list of strings

Question

In Python, I am using list(itertools.permutations("0123456789")) , and I am receiving (I as expected) a list of tuples of singled character strings.

Is there a way to turn that result into a list of strings, without iterating over all 3628800 items?

Answer 1

If you want to do it without iterating over the whole list but rather lazily doing it as needed, you can use itertools.imap :

itertools.imap(lambda x: "".join(x), itertools.permutations("0123456789"))

(note that I'm not using list() on the result of permutations here so it's as lazy as possible)

Or, as pointed out in the comments, a simple generator expression would work here as well:

("".join(x) for x in itertools.permutations("0123456789"))

itertools.imap has the additional benefit of being able to apply the same function on lots of iterables with a convenient syntax (simply adding them as subsequent arguments), but that's not necessary for this particular usage as we only have one iterable

Answer 2

Turning it into a list iterates over the whole thing. You can turn it into a list with a list comprehension, which will be better than turning it into a list then iterating over all the items of the list:

[''.join(item) for item in itertools.permutations('0123456789')]

If you don't need to end up with a list, a generator expression will suffice (replace [] with () ).