def _path_for_file(self, project_name, date):
return os.path.join(<EOL>self.cache_path,<EOL>'<STR_LIT>' % (project_name, date.strftime('<STR_LIT>'))<EOL>)<EOL>
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