Returns the constraints that have been accumulated since `other`.

        :param other: a prior PathHistory object
        :returns: a list of constraints

def constraints_since(self, other):
        """
        Returns the constraints that have been accumulated since `other`.

        :param other: a prior PathHistory object
        :returns: a list of constraints
        """

        constraints = [ ]
        cur = self
        while cur is not other and cur is not None:
            constraints.extend(cur.recent_constraints)
            cur = cur.parent
        return constraints