Re: [PATCH 08/12] qapi/schema: make QAPISourceInfo mandatory

[John Snow]

On 12/18/20 3:57 PM, Markus Armbruster wrote:
> John Snow <jsnow@redhat.com> writes:
>
> > On 12/18/20 12:24 AM, Markus Armbruster wrote:
> > > > I could conceivably use source line information and stuff, to be
> > > > needlessly fancy about it. Nah. I just think singleton patterns are kind
> > > > of weird to implement in Python, so I didn't.
> > > Stupidest singleton that could possibly work: in __init__,
> > > self.singleton = ...
> >
> > Yeah, you can make a class variable that has a builtin singleton, then
> > make the class method return that class variable.
> >
> > Feels fancier than my laziness permits. I just put it back to using
> > one copy per definition.
>
> Why have a class method around the attribute?  Just use the stoopid
> attribute already ;-P

Something has to initialize it:

```
class Blah:
    magic = Blah()

    def __init__(self):
        pass
```

Won't work; Blah isn't defined yet. a classmethod works though:

```
class Blah:
    magic = None

    def __init__(self) -> None:
        pass

    @classmethod
    def make(cls) -> 'Blah':
        if cls.magic is None:
            cls.magic = cls()
        return cls.magic
```