code: def generate_filename(self, requirement):
          
          return FILENAME_PATTERN % (self.config.cache_format_revision,
                                     requirement.name, requirement.version,
                                     get_python_version())
docs: Generate a distribution archive filename for a package.
  
          :param requirement: A :class:`.Requirement` object.
          :returns: The filename of the distribution archive (a string)
                    including a single leading directory component to indicate
                    the cache format revision.