All permutations from 2 lists

[Larry Martell]

On Wed, Mar 2, 2022 at 8:54 AM Joel Goldstick <joel.goldstick at gmail.com> wrote:
>
> On Wed, Mar 2, 2022 at 8:46 AM Larry Martell <larry.martell at gmail.com> wrote:
> >
> > 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.
> > --
> > https://mail.python.org/mailman/listinfo/python-list
>
> Does this help you out:
>
> >>> [(o,r) for o in opsys for r in region or "x"]
> [('Linux', 'x'), ('Window', 'x')]

That doesn't work if opsys = [] - either list could be empty.