variable

"breed": [
            {
                "$t": "Chihuahua"
            },
            {
                "$t": "Jack Russell Terrier"
            }
         ]

>>> o = [ { "$t": "Chihuahua" }, { "$t": "Jack Russell Terrier" } ]
>>> [ item["$t"] for item in o ]
['Chihuahua', 'Jack Russell Terrier']
>>>

nestedDict = { "breed": [
                        {
                         "$t": "Chihuahua"
                         },
                         {
                          "$t": "Jack Russell Terrier"
                          }
                         ]
              }

dictEntries = [ (k, v) for dicList in nestedDict.values() for d in dicList for (k, v) in d.items() ]

flattenedDict = { }
for k, v in dictEntries:
    flattenedDict.setdefault( k, [] ).append( v )

print ( flattenedDict )

{'$t': ['Chihuahua', 'Jack Russell Terrier']}

# Many thanks to Dogbert, whose answer I copied the list comprehension from
# (changing a few things), and many thanks to slothrop, whose answer gave me
# ideas for my variable name. Not for those people, I would have used a silly
# name like `thing` and would have used a for loop.
import json

nested_dict = json.loads('{"breed": [{"$t": "Chihuahua"}, '
                                    '{"$t": "Jack Russell Terrier"}]}')
[dic["$t"] for dic in nested_dict["breed"]]

key_and_value_pairs = []
for dic in nested_dict["breed"]:
    key_and_value_pairs.extend(dic.items())