bsearch.py

def bsearch(arr,key,start=0,end=None):
    if end == None: end = len(arr) - 1
    if start > end: return None
    if start == end and arr[start] != key: return None

    mid = (start+end)/2
    if arr[mid] == key:
        return mid
    if arr[mid] > key:
        return bsearch(arr,key,start,mid-1)
    if arr[mid] < key:
        return bsearch(arr,key,mid+1,end)