On 8/8/2019 7:28 PM, Barry Warsaw wrote:
On Aug 8, 2019, at 14:58, Steven D'Aprano <st...@pearwood.info> wrote:
It's not a syntax error. There's nothing wrong with the syntax per-say:
we still have ``target := expression``. There's a problem with the
*semantics* not the syntax.
I’m not sure that distinction is meaningful though. What you wrote is
disallowed, so you have to change your code (i.e. syntax) to avoid the error.
I agree with Barry here. For all practical purposes, it's a syntax
error. And if we had a more powerful parser, maybe it really would be a
syntax error. See Guido's recent PEG parser articles
(https://medium.com/@gvanrossum_83706/peg-parsers-7ed72462f97c) where he
discusses raising SyntaxError after the parser is finished, in a
subsequent pass. Is it really a syntax error if pgen doesn't object to
it? In current CPython, the answer is yes.
But to the original point: I think the real reason to make this just a
SyntaxError, and not a subclass (TargetScopeError) is this: would you
ever catch TargetScopeError? If not, why would it need to be its own
class? It should just be SyntaxError with a descriptive enough text that
the user can figure out what's wrong.
I don't see anyone ever writing:
try:
.. something ..
except TargetScopeError:
.. handle this ..
except SyntaxError:
.. handle this differently ..
Eric
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