code: def _search(mapping, filename):
      
      result = mapping.get(filename)
      if result is not None:
          return result
      name, ext = os.path.splitext(filename)
      result = mapping.get(ext)
      if result is not None:
          for pattern, result2 in result:
              if fnmatch(filename, pattern):
                  return result2
      return None
docs: Search a Loader data structure for a filename.