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

[Chris Angelico]

On Thu, Sep 27, 2018 at 3:31 PM Greg Ewing <greg.ewing at canterbury.ac.nz> wrote:
>
> Chris Angelico wrote:
> > if you let your API
> > docs rot when you make changes that callers need to be aware of, you
> > have failed your callers.
>
> Yes, I find that documentation auto-generated from code is
> usually a poor substitute for human-written documentation.
> Dumping your formally-written contracts into the docs makes
> the reader reverse-engineer them to figure out what the
> programmer was really trying to say.
>
> Which do you find easier to grok at a glance:
>
>     all(L[i] <= L[i+1] for i in range(len(L) - 1))
>
> or
>
>     # The list is now sorted
>

Well, with that particular example, you're capitalizing on the known
meaning of the English word "sorted". So to be fair, you should do the
same in Python:

postcondition: L == sorted(L)

This would be inappropriate for an actual sorting function, but let's
say you're altering the value of an item in a sorted list, and
shifting it within that list to get it to the new position, or
something like that.python-ideas <python-ideas at python.org>

But yes, in general I do agree: it's frequently cleaner to use an
English word than to craft a Python equivalent.

ChrisA