@Nullable
  public static PyType wrapInGeneratorType(@Nullable PyType elementType, @Nullable PyType returnType, @NotNull PsiElement anchor) {
    final PyClass generator = PyPsiFacade.getInstance(anchor.getProject()).createClassByQName(GENERATOR, anchor);
    return generator != null ? new PyCollectionTypeImpl(generator, false, Arrays.asList(elementType, null, returnType)) : null;
  }
@Nullable
  public static PyType wrapInGeneratorType(@Nullable PyType elementType, @Nullable PyType returnType, @NotNull PsiElement anchor)