assert list(filter(lambda x: ((x % 2) == 0), [0, 1, 2])) == [0, 2]
# None implies identity
assert list(filter(None, [0, 1, 2])) == [1, 2]
assert type(filter(None, [])) == filter
# test infinite iterator
class Counter(object):
counter = 0
def __next__(self):
self.counter += 1
return self.counter
def __iter__(self):
return self
it = filter(lambda x: ((x % 2) == 0), Counter())
assert next(it) == 2
assert next(it) == 4
def predicate(x):
if x == 0:
raise StopIteration()
return True
assert list(filter(predicate, [1, 2, 0, 4, 5])) == [1, 2]