A simple function to carry out a dichotomy search (the optimal search for an item's index in a sorted list), because it does not exist in the standard library.

dichotomy.py

def dichotomy(ls, v, _i=0):
    """ Dichotomy search, or the optimal search for an item's index
        in a sorted list.
        Arguments:
            - (list) ls: the list in which to search, must be sorted for
                this to work
            - v: value to search for in the list, must be comparable to the
                items in the list
            - (int) _i: should not be used, is reserved for recursive purposes
        Returns:
            The index of v in ls if found, -1 if not. The value
            returned is the first occurrence found, not guaranteed
            to be the first in the list
    """
    if ls == [] or ls is None:
        return -1
    midvalue = len(ls) // 2
    if v < ls[midvalue]:
        return dichotomy(ls[:midvalue], v, _i)
    elif v > ls[midvalue]:
        return dichotomy(ls[midvalue:], v, _i + midvalue)
    else:
        return _i + midvalue

This code is released under the .

As it turns out, python sucks at recursivity so I recommend finding or writing your own iterative implementation.