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I have a dictionary that had another dictionary and some lists inside that.

flightsD={"Delta":{1102:[["IND",1850],["MDW",1955]],

               1096:[["PHX",900],["MDW",1255]],

               1445:[["ATL",1135],["LAX",1810]],

               1776:[["PHL",1350],["RAP",1610]],

               1226:[["PHX",950],["MDW",1345]],

               1885:[["ATL",1305],["LAX",2000]],

               1009:[["MDW",1850],["IND",1955]],

               9001:[["MDW",2145],["IND",2255]]},

      "Southwestern":{1111:[["SAT",430],["MDW",825]],

                      2121:[["MDW",430],["SAT",825]],

                      4335:[["PHX",450],["MDW",745]],

                      1102:[["MDW",1100],["PHX",1450]]},

      "American":{7765:[["IND",1850],["CHA",2105]],

               2133:[["BNA",900],["IND",1115]],

               3321:[["HOU",1335],["ATL",1615]],

               2100:[["BNA",900],["IND",1115]],

               4311:[["HOU",905],["ATL",1255]],

               5577:[["ATL",1100],["HOU",1350]],

               1102:[["BNA",1100],["HOU",1450]]}  }

As you can see, Delta, Southwestern and American all have a flights 1102. I would like to list all duplicate flights as a list inside a dictionary.
Expected output:

{1102: ['American', 'Southwestern', 'Delta']}

I have tried to access these values by iterating through the dictionary like so:

for airline in flightsD:

    for flights in flightsD[airline]:

I am thinking about making a list to store all of these values but I'm not entirely sure how to go about it

You can iterate over the dict items, use dict.setdefault to initialize the output dict with a list to append airlines to, and use a dict comprehension to output items with sublists with more than 1 item:

d = {}

for airline, flights in flightsD.items():

    for flight in flights:

        d.setdefault(flight, ).append(airline)

print({k: v for k, v in d.items() if len(v) > 1})

This outputs:

{1102: ['Delta', 'Southwestern', 'American']}

You can use defaultdict as follows:

from collections import defaultdict



airlines, schedules = flightsD.keys(), flightsD.values()



flight_nums = [s.keys() for s in schedules]



duplicates = defaultdict(list)

for i, item1 in enumerate(flight_nums):

    for j, item2 in enumerate(flight_nums):       

        for k in item1:

            if i != j and k in item2 and airlines[i] not in duplicates[k]:

                duplicates[k].append(airlines[i])





print(duplicates)



>>> {1102: ['American', 'Southwestern', 'Delta']}

If you want a dictionary with just those values, you can use the code below (based on the code above):

list = 

for flights in flightsD.values():

    list.extend(flights.keys())



d = {}

for airline, flights in flightsD.items():

    for flight in flights:

        if list.count(flight) > 1:

            d.setdefault(flight, ).append(airline)