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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 _request(self, method, identifier, key=None, value=None):
 """Perform request with identifier."""

        params = {'id': identifier}
        if key is not None and value is not None:
            params[key] = value
        result = yield from self._transact(method, params)
        return result.get(key)