py-rioritized_methods is an extension to PEAK-Rules to prioritize
methods in order to avoid AmbiguousMethods situations.This module
provides four decorators:
    prioritized_when
    prioritized_around
    prioritized_before
    prioritized_after

These behave like their peak.rules counterparts except that they accept
an optional prio argument which can be used to provide a comparable
object (usually an integer) that will be used to disambiguate situations
in which more than rule applies to the given arguments and no rule is
more specific than another. That is, situations in which an
peak.rules.AmbiguousMethods would have been raised.

This is useful for libraries which want to be extensible via generic
functions but want their users to easily override a method without
figuring out how to write a more specific rule or when it is not
feasible.

WWW: https://pypi.python.org/pypi/prioritized_methods/