'Resolve the method on the parent filterset.'

@property
def method(self):

    instance = self.f
    if callable(instance.method):
        return instance.method
    assert hasattr(instance, u'parent'), (u"Filter    '%s'    must    have    a    parent    FilterSet    to    find    '.%s()'" % (instance.name, instance.method))
    parent = instance.parent
    method = getattr(parent, instance.method, None)
    assert callable(method), (u"Expected    parent    FilterSet    '%s.%s'    to    have    a    '.%s()'    method." % (parent.__class__.__module__, parent.__class__.__name__, instance.method))
    return method
