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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 fetch( self, request: Union["HTTPRequest", str], **kwargs: Any ) -> "HTTPResponse": """Executes a request, returning an `HTTPResponse`. The request may be either a string URL or an `HTTPRequest` object. If it is a string, we construct an `HTTPRequest` using any additional kwargs: ``HTTPRequest(request, **kwargs)`` If an error occurs during the fetch, we raise an `HTTPError` unless the ``raise_error`` keyword argument is set to False. """

        response = self._io_loop.run_sync(
            functools.partial(self._async_client.fetch, request, **kwargs)
        )
        return response