code: def mixed(self):
          
          result = {}
          multi = {}
          for key, value in self._items:
              if key in result:
                  # We do this to not clobber any lists that are
                  # *actual* values in this dictionary:
                  if key in multi:
                      result[key].append(value)
                  else:
                      result[key] = [result[key], value]
                      multi[key] = None
              else:
                  result[key] = value
          return result
docs: Returns a dictionary where the values are either single
          values, or a list of values when a key/value appears more than
          once in this dictionary.  This is similar to the kind of
          dictionary often used to represent the variables in a web
          request.