Pierre Reinbold wrote:
> Wow, thank you Ian for this very detailed answer, and thank you for taking
> the time for that! Much appreciated!
>
> If I get this right, I have to somehow fix the value of a_list during the
> loop, like when you use the classic default value argument trick with
> lambdas (damn, I should have thought of that!). So if I "unfold" the
> generator expression, using default values for both iterables, I get this
> :
>
> def flat_gen_cat_prod(lists):
> solutions = [[]]
> for a_list in lists:
> def new_solutions(l=a_list, s=solutions):
> for part_sol in s:
> for el in l:
> yield part_sol+[el]
> solutions = new_solutions()
> return solutions
>
> With this I get the right behavior! Thanks again!
>
> Doest that mean that there is no possibility to use a generator expression
> in this case ? (gen. exp. are sooo much more elegant :-))
The obvious approach is to put the genexpr into a function:
def prod(lists):
solutions = [[]]
def new_solutions(a_list):
return (part_sol + [el] for part_sol in solutions for el in a_list)
for a_list in lists:
solutions = new_solutions(a_list)
return solutions
If you want to avoid the function you can take advantage of the fact that
the outermost iterable is bound early:
def prod(lists):
solutions = [[]]
for a_list in lists:
solutions = (
part_sol + [el]
for solutions, a_list in [(solutions, a_list)]
for part_sol in solutions for el in a_list
)
return solutions
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