'Return the index in to the corresponding packfile for the object.
Given the name of an object it will return the offset that object
lives at within the corresponding pack file. If the pack file doesn\'t
have the object then None will be returned.'

def object_index(self, sha):

    if (len(sha) == 40):
        sha = hex_to_sha(sha)
    return self._object_index(sha)
