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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 _fetchOrFallback(self, _=None):
 """ Handles fallbacks for failure of fetch, wrapper for self._fetch """

        res = yield self._fetch(None)
        if res == RC_SUCCESS:
            return res
        elif self.retryFetch:
            yield self._fetch(None)
        elif self.clobberOnFailure:
            yield self.clobber()
        else:
            raise buildstep.BuildStepFailed()