def biggest(aDict):
'''
aDict: A dictionary, where all the values are lists.
returns: The key with the largest number of values associated with it
'''
return max(aDict, key=lambda x: len(aDict[x]))
animals = { 'a': ['aardvark'], 'b': ['baboon'], 'c': ['coati']}
animals['d'] = ['donkey']
animals['d'].append('dog')
animals['d'].append('dingo')
print(biggest(animals))
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