Question

For instance, lets say we call the function countPositive([1,2,3]), it will return a 3. Or if we have the array, [-1,0,1], there is one positive, so the function will return 1. So on, and so forth.

Answer 1

def countPositive(nums):
    return len(filter(lambda x: x > 0, nums))

Some timeit results (on a new macbook air w/1.8 i7, 4 gigs, and cpython 2.7):

filter + len:

$ python -m timeit "l = [-1, 0, 1] * 100; len(filter(lambda x: x > 0, l))"  
  10000 loops, best of 3: 49.9 usec per loop

$ python -m timeit "l = [-1, 0, 1] * 1000; len(filter(lambda x: x > 0, l))"                                                                  
1000 loops, best of 3: 476 usec per loop

$ python -m timeit "l = [-1, 0, 1] * 10000; len(filter(lambda x: x >  0, l))" 
100 loops, best of 3: 4.86 msec per loop

sum (recommended by hochl):

$ python -m timeit "l = [1, 2, 3] * 100; sum(1 for x in l if x > 0)" 
10000 loops, best of 3: 35.1 usec per loop

$ python -m timeit "l = [1, 2, 3] * 1000; sum(1 for x in l if x > 0)"
1000 loops, best of 3: 336 usec per loop

$ python -m timeit "l = [1, 2, 3] * 10000; sum(1 for x in l if x > 0)"
100 loops, best of 3: 3.4 msec per loop

So the sum version is slightly faster, but I think the len + filter is more readable.