Binary Search! - How would you write binary search?

bisect.py

def partition(nums, condition):
  """
  nums is ordered so that all the cases where condition is false at the beginning and it is true towards the end.
  We are tryng to find the first index where the condition is true.
  e.g
  nums = [1, 1, 1, 1, 2]
  condition = lambda val: val < 2
  partition will return 4
  """
  start = 0
  span = len(nums)
  while span:
    new_span = span>>1
    if start+new_span < len(nums) and not condition(nums[start+new_span]):
      start = start + (span - new_span)
    span = new_span
  return start
                     
                     
def bisect_left(nums, target):
  condition = lambda x < target
  return partition(nums, condition)

def bisect_right(nums, target):
  condition = lambda x <= target
  return partition(nums, condition)
                     
def binary_search(nums, target):
   index = bisect_left(nums, target)
   if index < len(nums) and nums[index]==target:
      return index
   return -1

found a bug in this.. haha