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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 df(self):
 """ Get data usage information. Returns: (dict):
 A dictionary representing different resource categories and their respective data usage. Raises: :py:class:`docker.errors.APIError` If the server returns an error. """

        url = self._url('/system/df')
        return self._result(self._get(url), True)