Thanks @tommyod.

I made the following changes:

• Renamed the function from bisect_right to find_stop
• The returned value is one higher than you had, for consistency with the other functions, like prefix_sum.
• Used a less strict criteria, but it can be modified with the strict argument
• Your PR had j = 2 ** len(self). That starts the search outside the bounds of the array, thus resulting in unnecessary computation (successive bit shifts). For example, with a length of 100, j would be set to 2 ** 100 = 1267650600228229401496703205376.
• The function now returns -1 for results that are out-of-range.

I've pushed the latest release to PyPI; it should be available now through pip.

Excellent, thanks!