python: many to many groupings using iterator module -

i have iterable, items of map multiple groups. how group items using iterator module?

animals = (human, frog, giraffe, fish) 

here human, frog, etc objects attributes: is_land_dwelling , is_water_dwelling.

i want group animals based on these attributes

groupings = dwelling_classifier(animals) 

should return group iterator splits animals into

is_land_dwelling: human, frog, giraffe is_water_dwelling: frog, fish 

i prefer make single pass on iterable. so, apart writing custom iterator function, there other way?

def is_water_dwelling(animal):     return animal in ('frog', 'fish')   def is_land_dwelling(animal):     return animal in ('frog', 'human', 'giraffe')  animals = ('human', 'frog', 'fish', 'giraffe')  land_dwelling = (x x in animals if is_land_dwelling(x)) water_dwelling = (x x in animals if is_water_dwelling(x))  print list(land_dwelling) print list(water_dwelling) 

note land_dwelling , water_dwelling generators.

this can generalized amount of "classifiers", holding relevant classification functions in dictionary of kind, possibly keyed classification type. (not tested):

kinds = {'water': is_water_dwelling, 'land': is_land_dwelling, 'air': is_flying} result = {}  kind, classifier in kinds.iteritems():   result[kind] = [x x in animals if classifier(x)]  # if want go on animals once, can instead: collections import defaultdict result = defaultdict(list)  x in animals:   kind, classifier in kinds.iteritems():     if classifier(x):       result[kind].append(x)