def _maybeGlobalReactor(maybeReactor):
    if maybeReactor is None:
        from twisted.internet import reactor
        return reactor
    else:
        return maybeReactor
This is pretty confusing, but there are two mechanisms for having a filter,
dataset/ETHPy150Open kuri65536/python-for-android/python-modules/twisted/twisted/application/internet.py/_maybeGlobalReactor--crossover with--dataset/ETHPy150Open dimagi/commcare-hq/corehq/ex-submodules/fluff/calculators.py/Calculator.passes_filter