gistfile1.py

from collections import defaultdict


phonebook = [('betty', '555-2938'),
             ('betty', '342-2492'),
             ('bonnie', '452-2928'),
             ('patsy', '493-2928'),
             ('patsy', '943-2929'),
             ('patsy', '827-9162'),
             ('lucille', '205-2928'),
             ('wendy', '939-8282'),
             ('penny', '853-2492'),
             ('penny', '555-2111')]

d = defaultdict(list)
[d[a].append(b) for a, b in phonebook]

dict(d) == {
    'lucille': ['205-2928'],
    'penny': ['853-2492', '555-2111'],
    'bonnie': ['452-2928'],
    'patsy': ['493-2928', '943-2929', '827-9162'],
    'betty': ['555-2938', '342-2492'],
    'wendy': ['939-8282']
}
# True