[Python-ideas] Pre-conditions and post-conditions

[Ivan Levkivskyi]

On Mon, 27 Aug 2018 at 11:39, Steven D'Aprano <steve at pearwood.info> wrote:

> On Mon, Aug 27, 2018 at 09:24:20AM +0100, Ivan Levkivskyi wrote:
> > TBH, I think one of the main points of design by contract is that
> contracts
> > are verified statically.
>
> No, that's not correct. Contracts may be verified statically if the
> compiler is able to do so, but they are considered runtime checks.
>

Considered by whom? By people who prefer `assert isinstance(x, int)` over
`x: int`? :-)

Contract in 99% of cases is just another word for type (maybe a very
complex type like `DAG[T] <: Graph[T]`).
Everything else, like `x >= y` is better expressed as an explicit assert
with an assert message.
But again this is rather IMO, than any kind of definition.

There is only one use case I see now where a dedicated syntax would give a
large readability gain:
something like `self.x >= self.y`. But on the other hand I think such
situations are too rare to justify any _new_ syntax.

--
Ivan
-------------- next part --------------
An HTML attachment was scrubbed...
URL: <http://mail.python.org/pipermail/python-ideas/attachments/20180827/924bc624/attachment.html>