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

Nikolas Vanderhoof nikolasrvanderhoof at gmail.com
Thu Jan 18 23:50:04 EST 2018

Thank you for your explanation!

On Thu, Jan 18, 2018 at 11:00 PM, Guido van Rossum <guido at python.org> wrote:

> On Thu, Jan 18, 2018 at 7:51 PM, Nikolas Vanderhoof <
> nikolasrvanderhoof at gmail.com> wrote:
>> I sometimes wish that Python included a richer set of assertions rather
>>> than just a single `assert` keyword. Something like Eiffel's concept of
>>> pre-conditions, post-conditions and invariants, where each can be
>>> enabled or disabled independently.
>> Has something like this been proposed for Python before?
>> This seems to align more with the intended use of assert that's been
>> pointed out in this thread.
>> In what case though would one want to disable some but not all of these
>> pre, post, or invariant assertions?
> Oh, many times, starting in the late '90s IIRC (Paul Dubois was a big fan).
> The problems are twofold: (a) it would require a lot of new keywords or
> ugly syntax; and (b) there would have to be a way to enable each form
> separately *per module or package*. Eiffel solves that (AFAIC) through
> separate compilation -- e.g. a stable version of a library might disable
> invariants and post-conditions but keep pre-conditions, since those could
> be violated by less mature application code; or a mature application could
> disable all checks and link with optimized library binaries that also have
> disabled all checks. I'm sure other scenarios are also viable.
> But that solution isn't available in Python, where command line flags
> apply to *all* modules being imported.
> (Note: even if you have a solution for (b), getting past (a) isn't so
> easy. So don't get nerd-sniped by the solution for (b) alone.)
> --
> --Guido van Rossum (python.org/~guido)
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