# Dictionaries are indexed by keys, which can be any immutable type;
# strings and numbers can always be keys.
# Tuples can be used as keys if they contain only strings, numbers, or tuples;
# if a tuple contains any mutable object either directly or indirectly,
# it cannot be used as a key.
# You can't use lists as keys, since lists can be modified.
# a dictionary is an unordered set of key: value pairs, with the requirement that the
# keys are unique (within one dictionary).
tel = {'jack': 4098, 'sape': 4139}
tel['guido'] = 4127
print tel
print tel['jack']
del tel['sape']
tel['irv'] = 4127
print tel
tel.keys()
print tel.has_key('guido')
print 'guido' in tel