code: def lookup(self, language_ranges):
          
          keys = list(self.keys())
          try:
              keys.remove(None)
          except ValueError:
              pass
          keys.sort()
          key = lookup_language(keys, language_ranges)
          return self[key]
docs: Perform an RFC4647 language range lookup on the keys in the
          dictionary. `language_ranges` must be a sequence of
          :class:`LanguageRange` instances.
  
          Return the entry in the dictionary with a key as produced by
          `lookup_language`. If `lookup_language` does not find a match and the
          mapping contains an entry with key :data:`None`, that entry is
          returned, otherwise :class:`KeyError` is raised.