[araooz]

Before:

>>> f(a=x := 1)
  File "<python-input-0>", line 1
    f(a=x := 1)
          ^^
SyntaxError: invalid syntax

After:

>>> f(a=x := 1)
  File "<python-input-0>", line 1
    f(a=x := 1)
        ^^^^^^
SyntaxError: cannot use named expression without parentheses here

This adds an alternative to invalid_kwarg that matches NAME '=' NAME ':=' expressionand reuses the message already used for assert x := 1. Because invalid_kwarg is used for all keyword arguments, this also covers keywords after positional, *args or **kwargs arguments, and class keywords such as class C(metaclass=x := type).

Unlike the patch suggested in the issue, the rule lives in invalid_kwarg instead of invalid_expression, so the existing messages for other cases (e.g. lambda and conditional expressions) are unchanged. Non-name targets like f(a=x.y := 1) keep the current message, since adding parentheses would not fix them.

Two existing tests in test_named_expressions (invalid_09 and invalid_10) asserted the generic "invalid syntax" message for exactly these inputs; they now expect the new message. New cases were added to test_syntax.

Related: #161927 handles the lambda case (gh-137570) with the same message.

• Issue: Specialize syntax error for assignment expressions in invalid places #146601

[python-cla-bot]

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