Lists aggregation

[Peter Otten]

mattia wrote:

> I have 2 lists, like:
> l1 = [1,2,3]
> l2 = [4,5]
> now I want to obtain a this new list:
> l = [(1,4),(1,5),(2,4),(2,5),(3,4),(3,5)]
> Then I'll have to transform the values found in the new list.
> Now, some ideas (apart from the double loop to aggregate each element of
> l1 with each element of l2):
> - I wanted to use the zip function, but the new list will not aggregate
> (3,4) and (3,5)
> - Once I've the new list, I'll apply a map function (e.g. the exp of the
> values) to speed up the process
> Some help?

Why would you keep the intermediate list?

With a list comprehension:

>>> a = [1,2,3]
>>> b = [4,5]
>>> [x**y for x in a for y in b]
[1, 1, 16, 32, 81, 243]

With itertools:

>>> from itertools import product, starmap
>>> from operator import pow
>>> list(starmap(pow, product(a, b)))
[1, 1, 16, 32, 81, 243]

Peter