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Solve the following problem using Python, implementing the functions described below, one line at a time
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Description:
 def override (overrider_id, overridee_id):
 """Make generator 'overrider-id' be preferred to 'overridee-id'. If, when searching for generators that could produce a target of certain type, both those generators are amoung viable generators, the overridden generator is immediately discarded. The overridden generators are discarded immediately after computing the list of viable generators, before running any of them."""

    assert isinstance(overrider_id, basestring)
    assert isinstance(overridee_id, basestring)

    __overrides.setdefault(overrider_id, []).append(overridee_id)