All permutations from 2 lists

[Larry Martell]

On Wed, Mar 2, 2022 at 9:10 AM Antoon Pardon <antoon.pardon at vub.be> wrote:
>
> Op 2/03/2022 om 14:44 schreef Larry Martell:
> > On Wed, Mar 2, 2022 at 8:37 AM Antoon Pardon<antoon.pardon at vub.be>  wrote:
> >>
> >> Op 2/03/2022 om 14:27 schreef Larry Martell:
> >>> On Tue, Mar 1, 2022 at 7:21 PM<2QdxY4RzWzUUiLuE at potatochowder.com>   wrote:
> >>>> On 2022-03-01 at 19:12:10 -0500,
> >>>> Larry Martell<larry.martell at gmail.com>   wrote:
> >>>>
> >>>>> If I have 2 lists, e.g.:
> >>>>>
> >>>>> os = ["Linux","Windows"]
> >>>>> region = ["us-east-1", "us-east-2"]
> >>>>>
> >>>>> How can I get a list of tuples with all possible permutations?
> >>>>>
> >>>>> So for this example I'd want:
> >>>>>
> >>>>> [("Linux", "us-east-1"), ("Linux", "us-east-2"), ("Windows",
> >>>>> "us-east-1"), "Windows", "us-east-2')]
> >>>>>
> >>>>> The lists can be different lengths or can be 0 length. Tried a few
> >>>>> different things with itertools but have not got just what I need.
> >>>> [(o, r) for o in os for r in region]
> >>> This does not work if region = []. I wrote in my question that either
> >>> list could be empty.
> >> What do you mean it doesn't work? The result seems to be an empty list,
> >> which IMO is a perfectly valid result.
> >>
> >> All possible permutations over two collections where one collection is
> >> empty, should IMO give you an empty collection.
> > If one list is empty I want just the other list. What I am doing is
> > building a list to pass to a mongodb query. If region is empty then I
> > want to query for just the items in the os list. I guess I can test
> > for the lists being empty, but I'd like a solution that handles that
> > as down the road there could be more than just 2 lists.
>
> How about the following: Keep a list of your lists you want to permute over.
> Like the following:
>
> permutation_elements = [["Linux","Windows"],["us-east-1", "us-east-2"]]
>
> permutation = itertools.product(*permutation_elements)
>
> If you don't include the empty list, you will get more or less what you
> seem to want.

But I need to deal with that case.