On 08/29/2018 04:53 PM, Hugh Fisher wrote:
From: Marko Ristin-Kaufmann:
There seems to be evidence that design-by-contract is useful. Let me cite
Bertrand Meyer from his article "Why not program right?" that I already
mentioned before:
I don't think that being useful by itself should be enough. I think new features
should also be "Pythonic" and I don't see design by contract notation as a
good fit.
I don't see type annotation notation as a good fit, either, and yet we have it. Seems to me that DbC would be just as
useful as type annotations (and I find D'Aprano's example syntax very readable).
For design by contract, as others have noted Python assert statements
work fine for simple preconditions and postconditions.
And print statements work fine for simple debugging. New features are not added for the simple cases, but the complex,
or non-obviously correct, or the very useful cases.
Yes there's more to design by contract than simple assertions, but it's not
just adding syntax. Meyer often uses the special "old" construct in his post
condition examples, a trivial example being
ensure count = old.count + 1
I can see where that could get expensive quickly.
How do we do that in Python? And another part of design by contract (at
least according to Meyer) is that it's not enough to just raise an exception,
but there must be a guarantee that it is handled and the post conditions
and/or invariants restored.
Well, we don't have to have exactly the same kind of DbC as Eiffel does.
--
~Ethan~
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