Transpose values and key in python dictionary when values are not unique [duplicate]

Answer 1

You can also do it with a defaultdict:

year_person = {2000: 'Linda', 2001: 'Ron', 2002: 'Bruce', 2003: 'Linda', 2004: 'Bruce', 2005: 'Gary', 2006: 'Linda'}

from collections import defaultdict
d = defaultdict(list)
for k, v in year_person.items():
    d[v].append(k)

print dict(d)
>>> {'Bruce': [2002, 2004], 'Linda': [2000, 2003, 2006], 'Ron': [2001], 'Gary': [2005]}