[Python-ideas] Why is design-by-contracts not widely adopted?

[Marko Ristin-Kaufmann]

Hi Chris,

An extraordinary claim is like "DbC can improve *every single project*
> on PyPI". That requires a TON of proof. Obviously we won't quibble if
> you can only demonstrate that 99.95% of them can be improved, but you
> have to at least show that the bulk of them can.


I tried to give the "proof" (not a formal one, though) in my previous
message. The assumptions are that:
* There are always contracts, they can be either implicit or explicit. You
need always to figure them out before you call a function or use its result.
* Figuring out contracts by trial-and-error and reading the code (the
implementation or the test code) is time consuming and hard.
* The are tools for formal contracts.
* The contracts written in documentation as human text inevitably rot and
they are much harder to maintain than automatically verified formal
contracts.
* The reader is familiar with formal statements, and hence reading formal
statements is faster than reading the code or trial-and-error.

I then went on to show why I think, under these assumptions, that formal
contracts are superior as a documentation tool and hence beneficial. Do you
think that any of these assumptions are wrong? Is there a hole in my
logical reasoning presented in my previous message? I would be very
grateful for any pointers!

If these assumptions hold and there is no mistake in my reasoning, wouldn't
that qualify as a proof?

Cheers,
Marko

On Tue, 25 Sep 2018 at 21:43, Chris Angelico <rosuav at gmail.com> wrote:

> On Wed, Sep 26, 2018 at 3:19 AM Marko Ristin-Kaufmann
> <marko.ristin at gmail.com> wrote:
> >> Claiming that DbC annotations will improve the documentation of every
> >> single library on PyPI is an extraordinary claim, and such claims
> >> require extraordinary proof.
> >
> >
> > I don't know what you mean by "extraordinary" claim and "extraordinary"
> proof, respectively. I tried to show that DbC is a great tool and far
> superior to any other tools currently used to document contracts in a
> library, please see my message
> https://groups.google.com/d/msg/python-ideas/dmXz_7LH4GI/5A9jbpQ8CAAJ.
> Let me re-use the enumeration I used in the message and give you a short
> summary.
> >
>
> An ordinary claim is like "DbC can be used to improve code and/or
> documentation", and requires about as much evidence as you can stuff
> into a single email. Simple claim, low burden of proof.
>
> An extraordinary claim is like "DbC can improve *every single project*
> on PyPI". That requires a TON of proof. Obviously we won't quibble if
> you can only demonstrate that 99.95% of them can be improved, but you
> have to at least show that the bulk of them can.
>
> > There are 150K projects on pypi.org. Each one of them would benefit if
> annotated with the contracts.
>
> This is the extraordinary claim. To justify it, you have to show that
> virtually ANY project would benefit from contracts. So far, I haven't
> seen any such proof.
>
> ChrisA
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