I think that Alex Martelli's answer is definitely the most elegant way to do this, but just wanted to add a way to satisfy your want for a super awesome dictionary.filter(f) method in a Pythonic sort of way:
class FilterDict(dict):
def __init__(self, input_dict):
for key, value in input_dict.iteritems():
self[key] = value
def filter(self, criteria):
for key, value in self.items():
if (criteria(value)):
self.pop(key)
my_dict = FilterDict( {'a':(3,4), 'b':(1,2), 'c':(5,5), 'd':(3,3)} )
my_dict.filter(lambda x: x[0] < 5 and x[1] < 5)
Basically we create a class that inherits from dict, but adds the filter method. We do need to use .items() for the the filtering, since using .iteritems() while destructively iterating will raise exception.