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

You have to iterate through the filter object somehow. One way is to convert it to a list:

l = list(filter(lambda x: x > 3, n))

len(l)  # <--

But that might defeat the point of using filter() in the first place, since you could do this more easily with a list comprehension:

l = [x for x in n if x > 3]

Again, len(l) will return the length.