How to find the length of a “filter” object in python

Question

>>> n = [1,2,3,4]

>>> filter(lambda x:x>3,n)


>>> len(filter(lambda x:x>3,n))
Traceback         


        

Answer 1

This is an old question, but I think this question needs an answer using the map-reduce ideology. So here:

from functools import reduce

def ilen(iterable):
    return reduce(lambda sum, element: sum + 1, iterable, 0)

ilen(filter(lambda x: x > 3, n))

This is especially good if n doesn't fit in the computer memory.