Python 3 preparation: avoid assigning to instance __getitem__ in TruthDict. In Python 3, special method names are generally only looked up at the class level, not on instance objects, and so assigning to them for an instance object doesn't work as expected.

try:
    # Python 2.
    my_input = raw_input
except NameError:
    # Python 3+.
    my_input = input