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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 useKeyID(self, keyID):
 """ Use the given API key config specified by `keyID` during subsequent API calls :param str keyID: an index into the 'keys' maintained in this config """

        if keyID not in self._data['keys']:
            raise ConfigException('keyID does not exist: %s' % keyID)
        self._keyID = keyID