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

[Nikolas Vanderhoof]

I think having a means for such validations separate from assertions would
be helpful.
However, I agree with Steven that 'validate' would be a bad keyword choice.
Besides breaking compatibility with programs that use 'validate', it would
break
wsgiref.validate
<https://docs.python.org/3.6/library/wsgiref.html#module-wsgiref.validate>
in the standard library.

ᐧ

On Tue, Jan 16, 2018 at 2:22 PM, Juancarlo Añez <apalala at gmail.com> wrote:

> 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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