variable X procuct - [(x,y) for x in list1 for y in list2]

[Chris Liechti]

steindl fritz <python at floSoft.org> wrote in 
news:1022619068.34271 at newsmaster-04.atnet.at:
> first - maybe sombody can help me with the english expression for the 
> german word 'kreuzprodukt' - this my question is dealing with

try: http://dict.tu-chemnitz.de/
"cross product"
 
> -----------------------------------------------
> 
> example -
> 
> list1 = [1, 2]
> list2 = [a, b, c]
> 
> [(x,y) for x in list1 for y in list2]
> 
> the result is the "kreuzprodukt"
> [(1,a), (1,b), (1,c), (2,a), (2,b), (2,c)]
> 
> -----------------------------------------------
> 
> question -
> 
> i need to keep the number of lists variable
> 
> e.g. the next case should handle three lists
> 
> [(a1, a2, a3) for a1 in list1 for a2 in list2 for a3 in list3]
> 
> i cannot put variables into this algorythm or they don't do what i expect
> maybe there is a simple solution, but i cannot find it 

you're sure you want to program this yourself? there is numpy, i think it 
can handle that.

anyway, this one is taking list of list (or tuples):
>>> xp=lambda l1,l2:[x+y for x in l1 for y in l2]

>>> xp([(1, 'a'), (2, 'b')], [(1, 'a'), (2, 'b')])
[(1, 'a', 1, 'a'), (1, 'a', 2, 'b'), (2, 'b', 1, 'a'), (2, 'b', 2, 'b')]

zip can be used to transform a list to a list of list (trasposed)
that way you can use it nested:

>>> xp(xp(zip([1,2]), zip([a,b,c])), zip([3,4]))

chris

-- 
Chris <cliechti at gmx.net>