I just read your e-mail (before reading any follow up here), fired up
Python 3.8 and typed in
what I thought would be an ambiguous or confuse case, withut checking the
PEP.
the result:
```
Python 3.8.0b3+ (heads/3.8:ef0b81927a, Aug 6 2019, 20:30:57)
Type 'copyright', 'credits' or 'license' for more information
IPython 7.7.0 -- An enhanced Interactive Python. Type '?' for help.
In [1]: class A:
...: b = 0
...: any((b:= i, 0)[1] for i in range(10))
File "<ipython-input-1-22c303b71775>", line 3
any((b:= i, 0)[1] for i in range(10))
^
TargetScopeError: named expression within a comprehension cannot be used in
a class body
```
So, while the name "TargetScopeError" can sound confusing,
I think the extended error message could not be more
clear and unambiguous. It seems just fine as it is.
On Thu, 8 Aug 2019 at 14:02, Barry Warsaw <ba...@python.org> wrote:
> 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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