Search code examples
pythonlisttupleslist-comprehension

Python - Write all tuples of a combination using list comprehension

I would like to create all pairs (i, j) such that i goes from 0 to n-1 and j goes from i to n-1. Basically these are all the unique combinations for two lists of length n.

As an example if n=3 then I would like to get

[(0, 0), (0, 1), (0, 2), (1, 1), (1, 2), (2, 2)]

It would be great if I could do this with a list comprehension. The long way around would be

n = 3
tuples = []
for i in range(n):
    for j in range(i, n):
         tuples.append((i, j))

I have tried this list comprehension, unsuccessfully

tuples = [(i,j) for i in range(3) and j in range(i, 3)]
Solution

  • Just switch the order of your loops:

    tuples = [(i,j) for i in range(3) for j in range(i, 3)]

    Output:

    Out[425]: [(0, 0), (0, 1), (0, 2), (1, 1), (1, 2), (2, 2)]