def iFilter(fn, li):
  result = []
  for x in li:
    if fn(x): 
      result.append(x)
  return result 

def rFilter(fn, li):
  if len(li) == 0: return []
  head, *tail = li 
  if fn(head): 
    return [head] + rFilter(fn, tail)
  return rFilter(fn, tail)

li = [1, 2, 3, 4, 5, 6]
print('input list:', li)

odds = iFilter(lambda x: x % 2, li)
evens = iFilter(lambda x: not (x % 2), li)
print('\nusing iterative filter function')
print('odds :', odds)
print('evens:', evens)

print('\nusing recursive filter function')
odds = rFilter(lambda x: x % 2, li)
evens = rFilter(lambda x: not (x % 2), li)
print('odds :', odds)
print('evens:', evens)