Combinations or Permutations

[Seth Leija]

I need to know how to generate a list of combinations/permutations
(can't remember which it is). Say I have a list of variables:

[a,b,c,d,...,x,y,z]

I am curious if there is an optimized way to generate this:

[[a,b],[a,c],[a,d],...,[x,z],[y,z]]

I currently have an iteration that does this:

#list.py

from math import *

list1=['a','b','c','d','e']
list2=[]
length=len(list1)

for it1 in range(0 ,length):
    for it2 in range(it1+1, length):
        list2.append([list1[it1],list1[it2]])

print list2

However, this is one of the slowest parts of my function (beaten only
by variable instantiation). I posted this on another forum looking to
see if there was a different method completely. They said that my
method was about as simple as it could get, but I might be able to
find out how to optimize my code here.

Thanks in advance.