[Python-Dev] PEP 492 vs. PEP 3152, new round

[Isaac Schwabacher]

On 15-04-29, Yury Selivanov  wrote:
> 
> 
> On 2015-04-29 3:24 PM, Isaac Schwabacher wrote:
> >On 15-04-29, Yury Selivanov wrote:
> >>Hi Ethan,
> [..]
> >>So I want to make this syntactically incorrect:
> >Does this need to be a syntax error? -"hello" raises TypeError because str doesn't have a __neg__, but there's no reason a str subclass couldn't define one. "TypeError: bad operand type for unary -: 'asyncio.Future'" is enough to clear up any misunderstandings, and if someone approaching a new language construct doesn't test their code well enough to at least execute all the code paths, the difference between a compile-time SyntaxError and a run-time TypeError is not going to save them.
> 
> The grammar of the language should match the most common
> use case.
> 
> FWIW, I've just updated the pep with a precedence table:
> https://hg.python.org/peps/rev/d355918bc0d7

I'd say the grammar of the language should be the least surprising overall, which definitely means it should be clean in the most common case but doesn't mean it has to go out of its way to make other cases difficult. But reading that precedence table makes everything clear-- the proper comparison isn't (-"hello"), it's (-not False), which *is* a syntax error. Silly prefix operators.

ijs