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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 requests_usage(self, year=None, month=None):
 """ Retrieves Cloudant requests usage data, optionally for a given year and month. :param int year: Year to query against, for example 2014. Optional parameter. Defaults to None. If used, it must be accompanied by ``month``. :param int month: Month to query against that must be an integer between 1 and 12. Optional parameter. Defaults to None. If used, it must be accompanied by ``year``. :returns: Requests usage data in JSON format """

        endpoint = '/'.join((
            self.server_url, '_api', 'v2', 'usage', 'requests'))
        return self._usage_endpoint(endpoint, year, month)