code: def create_map(self, type_from, type_to, mapping=None):
          
          key_from = type_from.__name__
          key_to = type_to.__name__
  
          if mapping is None:
              mapping = {}
  
          if key_from in self.mappings:
              inner_map = self.mappings[key_from]
              if key_to in inner_map:
                  raise ObjectMapperException("Mapping for {0} -> {1} already exists".format(key_from, key_to))
              else:
                  inner_map[key_to] = mapping
          else:
              self.mappings[key_from] = {}
              self.mappings[key_from][key_to] = mapping
docs: Method for adding mapping definitions
  
          :param type_from: source type
          :param type_to: target type
          :param mapping: dictionary of mapping definitions in a form {'target_property_name',
                          lambda function from rhe source}
  
          :return: None