[Python-ideas] Repurpose `assert' into a general-purpose check

[Juancarlo Añez]

Perhaps the OP can look into Python macro libraries to get the wanted
syntax?

https://github.com/lihaoyi/macropy

On Tue, Jan 16, 2018 at 2:35 PM, Paul Moore <p.f.moore at gmail.com> wrote:

> On 16 January 2018 at 17:36, Sylvain MARIE
> <sylvain.marie at schneider-electric.com> wrote:
> > (trying with direct reply this time)
> >
> >> Why do you do this? What's the requirement for delaying evaluation of
> the condition?
> >
> > Thanks for challenging my poorly chosen examples :)
> >
> > The primary requirement is about *catching* unwanted/uncontrolled/heterogenous
> exceptions happening in the underlying functions that are combined together
> to provide the validation means, so as to provide a uniform/consistent
> outcome however diverse the underlying functions are (they can return
> booleans or raise exceptions, or both).
> >
> > In your proposal, if 'is_foo_compliant' raises an exception, it will not
> be caught by 'assert_valid', therefore the ValidationError will not be
> raised. So this is not what I want as an application developer.
>
> Ah, OK. But nothing in your proposal for a new statement suggests you
> wanted that, and assert doesn't work like that, so I hadn't realised
> that's what you were after.
>
> You could of course simply do:
>
> def assert_valid(expr, help_msg):
>     # Catch exceptions in expr() as you see fit
>     if not expr():
>         raise ValidationError(help_msg)
>
> assert_valid(lambda: 0 <= surf < 10000 and is_foo_compliant(surf),
>     help_msg="surface should be 0=<x<10000 or foo compliant")
>
> No need for a whole expression language :-)
>
> Paul
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-- 
Juancarlo *Añez*
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