On 8/29/2018 6:39 PM, Eric Fahlgren wrote:
On Wed, Aug 29, 2018 at 3:07 PM Marko Ristin-Kaufmann
<marko.ris...@gmail.com <mailto:marko.ris...@gmail.com>> wrote:
Could you please elaborate a bit? I don't see how the annotations
would make the contracts invoked on inheritance. Consider this
simple case:
class A:
@icontract.pre(lambda x: x > 0)
def some_method(self, x: int)->None:
pass
class B(A):
# Precondition should be inherited here.
def some_method(self, x: int) -> None:
pass
You would still need to somehow decorate manually the overridden
methods even though you would not specify any new contracts, right?
Is there a mechanism in Python that I am not aware of that would
allow us to accomplish that?
A metaclass does this pretty easily. I have a thing I wrote years ago
called MIS (Multi-Inheritance Safety) that is used to ensure you don't
do anything stupid in our physics-modeling database. The database is a
collection of ~200 Python classes/mixins all deriving madly from each
other to get various behaviors (Has mass? You'll need this. Has
moments? You'll need this. Has physical extent, i.e., can be seen?
You'll need these...).
I think a metaclass is a non-starter. If one were used, it would
preclude using contracts in any case where a metaclass were already
used, or where one was needed in the future. I'm sure people will
disagree with me on this.
But, I think a more productive line of thinking is: what could be added
to the language that would let contracts be implementable, and could
also be used for other things, too? Sort of like how PEP 487 adds
customizability that has wide applicability.
Eric
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