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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 _path_for_file(self, project_name, date):
 """ Generate the path on disk for a specified project and date. :param project_name: the PyPI project name for the data :type project: str :param date: the date for the data :type date: datetime.datetime :return: path for where to store this data on disk :rtype: str """

        return os.path.join(
            self.cache_path,
            '%s_%s.json' % (project_name, date.strftime('%Y%m%d'))
        )