Re: [PATCH 05/19] qapi/schema: make c_type() and json_type() abstract methods

[Daniel P . Berrangé]

On Tue, Nov 21, 2023 at 11:28:17AM -0500, John Snow wrote:
> On Tue, Nov 21, 2023, 8:43 AM Daniel P. Berrangé <berrange@redhat.com>
> wrote:
> 
> > On Tue, Nov 21, 2023 at 02:36:54PM +0100, Markus Armbruster wrote:
> > > John Snow <jsnow@redhat.com> writes:
> > >
> > > > These methods should always return a str, it's only the default
> > abstract
> > > > implementation that doesn't. They can be marked "abstract" by raising
> > > > NotImplementedError(), which requires subclasses to override the method
> > > > with the proper return type.
> > > >
> > > > Signed-off-by: John Snow <jsnow@redhat.com>
> > > > ---
> > > >  scripts/qapi/schema.py | 8 ++++----
> > > >  1 file changed, 4 insertions(+), 4 deletions(-)
> > > >
> > > > diff --git a/scripts/qapi/schema.py b/scripts/qapi/schema.py
> > > > index c5fdd625452..4600a566005 100644
> > > > --- a/scripts/qapi/schema.py
> > > > +++ b/scripts/qapi/schema.py
> > > > @@ -233,8 +233,8 @@ def visit(self, visitor):
> > > >  class QAPISchemaType(QAPISchemaEntity):
> > > >      # Return the C type for common use.
> > > >      # For the types we commonly box, this is a pointer type.
> > > > -    def c_type(self):
> > > > -        pass
> > > > +    def c_type(self) -> str:
> > > > +        raise NotImplementedError()
> > > >
> > > >      # Return the C type to be used in a parameter list.
> > > >      def c_param_type(self):
> > > > @@ -244,8 +244,8 @@ def c_param_type(self):
> > > >      def c_unboxed_type(self):
> > > >          return self.c_type()
> > > >
> > > > -    def json_type(self):
> > > > -        pass
> > > > +    def json_type(self) -> str:
> > > > +        raise NotImplementedError()
> > > >
> > > >      def alternate_qtype(self):
> > > >          json2qtype = {
> > >
> > > I wish abstract methods could be done in a more concise way.
> >
> > The canonical way would be to use the 'abc' module:
> >
> >   from abc import ABCMeta, abstractmethod
> >
> >   class A(metaclass=ABCMeta):
> >       @abstractmethod
> >       def foo(self): pass
> >
> > Not sure if the @abstractmethod decorator is enough to keep the static
> > typing checker happy about a 'str' return type, when there is no body
> > impl
> 
> In practice, I'm under the belief that mypy and pylint both recognize a
> method raising NotImplementedError as marking an abstract method without
> needing to explicitly inherit from the ABC.
> 
> I suppose there's also
> https://docs.python.org/3/library/abc.html#abc.abstractmethod which I am
> guessing just does this same thing. I'll see what makes mypy happy. I'm
> assuming Markus would like to see something like this decorator to make it
> more obvious that it's an abstract method.

The 'abc' module described is an official PEP standard

  https://peps.python.org/pep-3119/

With regards,
Daniel
-- 
|: https://berrange.com      -o-    https://www.flickr.com/photos/dberrange :|
|: https://libvirt.org         -o-            https://fstop138.berrange.com :|
|: https://entangle-photo.org    -o-    https://www.instagram.com/dberrange :|