[Python-Dev] Pragmas and warnings

[M.-A. Lemburg]

Paul Prescod wrote:
> 
> A couple of other threads started me to thinking that there are a couple
> of things missing from our warnings framework.
> 
> Many languages have pragmas that allow you turn warnings on and off in
> code. For instance, I should be able to put a pragma at the top of a
> module that uses string functions to say: "I know that this module
> doesn't adhere to the latest Python conventions. Please don't warn me
> about it." I should also be able to put a declaration that says: "I'm
> really paranoid about shadowing globals and builtins. Please warn me
> when I do that."
> 
> Batch and visual linters could also use the declarations to customize
> their behaviors.
> 
> And of course we have a stack of other features that could use pragmas:
> 
>  * type signatures
>  * Unicode syntax declarations
>  * external object model language binding hints
>  * ...
> 
> A case could be made that warning pragmas could use a totally different
> syntax from "user-defined" pragmas. I don't care much.

There was a long thread about this some months ago. We agreed
to add a new keyword to the language (I think it was "define")
which then uses a very simple syntax which can be interpreted 
at compile time to modify the behaviour of the compiler, e.g.

define <identifier> = <literal>

There was also a discussion about allowing limited forms of
expressions instead of the constant literal.

define source_encoding = "utf-8"

was the original motivation for this, but (as always ;) the
usefulness for other application areas was quickly recognized, e.g.
to enable compilation in optimization mode on a per module
basis.

PS: "define" is perhaps not obscure enough as keyword...

-- 
Marc-Andre Lemburg
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