Creating a dictionary from another dictionary where keys' = (values in previous dictionary) and value' = (shared values in previous dictionary)

I have a dictionary set up as movie: {actors}. Below is a snippet of this dictionary

movie_dict = {
    'Sleepers': {'Brad Pitt', 'Kevin Bacon', 'Dustin Hoffman'}, 
    'Troy': {'Brad Pitt', 'Diane Kruger'}, 
    'Meet Joe Black': {'Brad Pitt', 'Anthony Hopkins'}, 
    'Oceans Eleven': {'Julia Roberts', 'Brad Pitt', 'George Clooney'}, 
    'Seven': {'Brad Pitt', 'Morgan Freeman'}
}

I am trying to create a dictionary of Co-Stars so that every actor is a key, and its values are a set of its costars.

Thanks in advance for any help! 🙂

>Solution :

You could use collections.defaultdict:

>>> from collections import defaultdict
>>> movie_dict = {
...     'Sleepers': {'Brad Pitt', 'Kevin Bacon', 'Dustin Hoffman'},
...     'Troy': {'Brad Pitt', 'Diane Kruger'},
...     'Meet Joe Black': {'Brad Pitt', 'Anthony Hopkins'},
...     'Oceans Eleven': {'Julia Roberts', 'Brad Pitt', 'George Clooney'},
...     'Seven': {'Brad Pitt', 'Morgan Freeman'}
... }
>>> costars = defaultdict(set)
>>> for actors in movie_dict.values():
...     for actor in actors:
...         costars[actor] |= actors - {actor}
...
>>> for actor, actors_costars in costars.items():
...      print(f'{actor}: {actors_costars}')
...
Brad Pitt: {'Anthony Hopkins', 'George Clooney', 'Julia Roberts', 'Diane Kruger', 'Dustin Hoffman', 'Kevin Bacon', 'Morgan Freeman'}
Kevin Bacon: {'Brad Pitt', 'Dustin Hoffman'}
Dustin Hoffman: {'Brad Pitt', 'Kevin Bacon'}
Diane Kruger: {'Brad Pitt'}
Anthony Hopkins: {'Brad Pitt'}
George Clooney: {'Julia Roberts', 'Brad Pitt'}
Julia Roberts: {'George Clooney', 'Brad Pitt'}
Morgan Freeman: {'Brad Pitt'}