code: def cache_distribution(cls, zf, source, target_dir):
      
      dependency_basename = os.path.basename(source)
      if not os.path.exists(target_dir):
        target_dir_tmp = target_dir + '.' + uuid.uuid4().hex
        for name in zf.namelist():
          if name.startswith(source) and not name.endswith('/'):
            zf.extract(name, target_dir_tmp)
        os.rename(os.path.join(target_dir_tmp, source),
                  os.path.join(target_dir_tmp, dependency_basename))
  
        rename_if_empty(target_dir_tmp, target_dir)
  
      dist = DistributionHelper.distribution_from_path(target_dir)
      assert dist is not None, 'Failed to cache distribution %s' % source
      return dist
docs: Possibly cache an egg from within a zipfile into target_cache.
  
         Given a zipfile handle and a filename corresponding to an egg distribution within
         that zip, maybe write to the target cache and return a Distribution.