bpo-37757: https://bugs.python.org/issue37757

This issue describes some corner cases in PEP 572 (assignment expressions) syntax that haven’t been implemented yet.  The PEP currently says:

"The two invalid cases listed above raise TargetScopeError, a new subclass of SyntaxError (with the same signature).”

The PEP doesn’t really go into the rationale for why a new exception is being defined, and in the issue I’ve argued that we should just raise SyntaxError in those cases.  To me, “TargetScopeError” is pretty obscure and doesn’t give users an obvious clue as to what’s going wrong, without searching the interwebs.

Nick argues (apologies if I’m misrepresenting you!):

"I believe our main motivation for separating it out was the fact that even though TargetScopeError is a compile-time error, the affected code is syntactically fine - there are just issues with unambiguously inferring the intended read/write location for the affected target names. (Subclassing SyntaxError is then a pragmatic concession to the fact that "SyntaxError" also de facto means "CompilationError”)”

Serhiy points out that we have IndentationError and TabError subclasses of SyntaxError, but those feel different to me because the exception names themselves are clear and descriptive, and lead to obvious actionable remedies.

Guido then suggests we take the discussion here, thus this email.

It would be a very minor update to the PEP, but I think it’s useful to resolve before the last push for PEP 572 implementation gets completed.

Rather than just a vote, if you have a rationale for one over the other, I’d love to hear it.  Feel free to weigh in here or on the issue.

Cheers,
-Barry

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