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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 _store_cached_source_variable(self, source_id, name, value):
 """ Stores the current known value of a source variable into the cache. Calls any source callbacks. """

        source_state = self._source_state.setdefault(source_id, {})
        name = name.lower()
        source_state[name] = value
        logger.debug("Source Cache store S[%d].%s = %s",
                     source_id, name, value)
        for callback in self._source_callbacks:
            callback(source_id, name, value)