docs: def reverse_list_valued_dict(dict_obj):
      """Reverse a list-valued dict, so each element in a list maps to its key.
  
      Parameters
      ----------
      dict_obj : dict
          A dict where each key maps to a list of unique values. Values are
          assumed to be unique across the entire dict, on not just per-list.
  
      Returns
      -------
      dict
          A dict where each element in a value list of the input dict maps to
          the key that mapped to the list it belongs to.
  
      Example
      -------
      >>> dicti = {'a': [1, 2], 'b': [3, 4]}
      >>> reverse_list_valued_dict(dicti)
      {1: 'a', 2: 'a', 3: 'b', 4: 'b'}
      """
      new_dict = {}
      for key in dict_obj:
          for element in dict_obj[key]:
              new_dict[element] = key
      return new_dict