Commutative combination of elements of two lists

Question

Just a style question: Is there a build-in method to get the combinations under the assertion of commutative property and excluding elements paired with itself?

Answer 1

Probably the simplest and most explicit (i.e. self-explanatory) solution is this I think:

>>> for i in range(len(a)): 
...     for j in range(i+1, len(b)): 
...         print(a[i], a[j]) 
... 
1 2
1 3
2 3

Unless you're doing something very fast in the inner loop, the inefficiency of the python for loops will hardly be a bottleneck.

Or, this:

>>> [(a[i], b[j]) for i in range(len(a)) for j in range(i+1, len(b))]
[('1', '2'), ('1', '3'), ('2', '3')]