code: def bind(self, typevar, its_type):
          
          assert type(typevar) == tg.TypeVar
          if self.is_generic_in(typevar):
              self.bind_to_instance(typevar, its_type)
          else:
              self._ns[typevar] = its_type
docs: Binds typevar to the type its_type.
          Binding occurs on the instance if the typevar is a TypeVar of the
          generic type of the instance, on call level otherwise.