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

[John Snow <jsnow@redhat.com>]

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
```