On 2024-02-17 22:35, Jonathan Gossage via Python-list wrote:
I am attempting to use the __new__ method in the following code:
class SingletonExample(object):

     _instance = None

     def __new__(cls, **kwargs):
         if cls._instance is None:
             cls._instance = super().__new__(cls, **kwargs)
         return cls._instance

     def __init__(self, **kwargs) -> None:
         our_attributes = ('h', 'x')
         if kwargs is not None:
             for k, v in kwargs.items():
                 if k in our_attributes:
                     setattr(self, k, v)

a = SingletonExample(h=1)

and I get the following result:

(PRV) jonathan@jfgdev:/PR$ python -m Library.Testing.test2
Traceback (most recent call last):
   File "<frozen runpy>", line 198, in _run_module_as_main
   File "<frozen runpy>", line 88, in _run_code
   File "/mnt/ProgrammingRenaissance/Library/Testing/test2.py", line 16, in
     a = SingletonExample(h=1)
   File "/mnt/ProgrammingRenaissance/Library/Testing/test2.py", line 6, in
     cls._instance = super().__new__(cls, **kwargs)
TypeError: object.__new__() takes exactly one argument (the type to

I am quite puzzled as it looks as if this code will not work if the
super-class is 'object'. Any suggestions on how to proceed?

Don't pass kwargs to object.__new__ because it doesn't expect it.

Incidentally, kwargs will never be None, and there's no point in giving a return type for __init__ because it can only ever return None.

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