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

["Daniel P. Berrangé" <berrange@redhat.com>]

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

With regards,
Daniel
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