I understand there are many, many posts about permutations (unique, variable length, etc.), but I have not been able to use them to solve my particular issue.

Let's say I have a list of metropolitan areas in the United States: ['nyc','sf','atl']

I need to output a permutation of 2 metros without repetition. For example, I've tried:

set(itertools.permutations(['nyc','sf','atl'], 2)){('atl', 'nyc'),('atl', 'sf'),('nyc', 'atl'),('nyc', 'sf'),('sf', 'atl'),('sf', 'nyc')}

However, notice that NYC and ATL are paired twice: ('nyc', 'atl') and ('atl', 'nyc'). The ideal output would be:

{('nyc', 'nyc'),('nyc', 'sf'),('nyc', 'atl'),('sf', 'sf'),('sf', 'atl'),('atl', 'atl')}

As mentioned by @Daniel Mesejo comment, use combinations.

>>> import itertools
>>> set(itertools.combinations(['nyc','sf','atl'], 2))
{('nyc', 'atl'), ('sf', 'atl'), ('nyc', 'sf')}