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counting odd numbers in a list python

This is a part of my homework assignment and im close to the final answer but not quite yet. I need to write a function that counts odd numbers in a list.

Create a recursive function count_odd(l) which takes as its only argument a list of integers. The function will return a count of the number of list elements that are odd, i.e., not evenly divisible by 2.

>>> print count_odd([])  
0  
>>> print count_odd([1, 3, 5])  
3  
>>> print count_odd([2, 4, 6])  
0  
>>> print count_odd([0, 1, 1, 2, 3, 5, 8, 13, 21, 34, 55, 89, 144])  
8

Here is what i have so far: #- recursive function count_odd -#

def count_odd(l):
    """returns a count of the odd integers in l.
    PRE: l is a list of integers.
    POST: l is unchanged."""
    count_odd=0

    while count_odd<len(l):
        if l[count_odd]%2==0:
            count_odd=count_odd
        else:
            l[count_odd]%2!=0
            count_odd=count_odd+1
    return count_odd

#- test harness  
print count_odd([])  
print count_odd([1, 3, 5])  
print count_odd([2, 4, 6])  
print count_odd([0, 1, 1, 2, 3, 5, 8, 13, 21, 34, 55, 89, 144])

Can u help explain what im missing. The first two test harness works fine but i cant get the final two. Thanks!

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Answer

Are slices ok? Doesn’t feel recursive to me, but I guess the whole thing is kind of against usual idioms (i.e. – recursion of this sort in Python):

def countOdd(l):
    if l == list(): return 0           # base case, empty list means we're done
    return l[0] % 2 + countOdd(l[1:])  # add 1 (or don't) depending on odd/even of element 0.  recurse on the rest

x%2 is 1 for odds, 0 for evens. If you are uncomfortable with it or just don’t understand it, use the following in place of the last line above:

   thisElement = l[0]
   restOfList = l[1:]
   if thisElement % 2 == 0: currentElementOdd = 0
   else: currentElementOdd = 1
   return currentElementOdd + countOdd(restOfList)

PS – this is pretty recursive, see what your teacher says if you turn this in =P

>>> def countOdd(l):
...     return fold(lambda x,y: x+(y&1),l,0)
... 
>>> def fold(f,l,a):
...     if l == list(): return a
...     return fold(f,l[1:],f(a,l[0]))
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