Python static class variable in nested class

Question

I have a nested class that uses static vars to have class wide parameters and accumulators.

If I do it as a standalone class it works.

If I do a nested class and inherit the standalone class, it works.

But I can't get a nested class to have static class variables, the interpreter gets confused. What am I doing wrong?

Code snippet:

class Cl_static_parameter_standalone: #static var common to all instances. Two uses: common settings, common accumulator c_n_counter : int = 0 @staticmethod def increment() -> int: Cl_static_parameter_standalone.c_n_counter += 1 return Cl_static_parameter_standalone.c_n_counter class Cl_some_class: class Cl_static_parameter_inherited(Cl_static_parameter_standalone): pass class Cl_static_parameter_nested: c_n_counter : int = 0 @staticmethod def increment() -> int: Cl_static_parameter_nested.c_n_counter += 1 return Cl_static_parameter_nested.c_n_counter def __init__(self): return def do_something(self): print(f"Execute Standalone: {Cl_static_parameter_standalone.increment()}") print(f"Execute Inherited: {self.Cl_static_parameter_inherited.increment()}") print(f"Execute Nested: {self.Cl_static_parameter_nested.increment()}") return my_instance = Cl_some_class() my_instance.do_something()

Output:

Execute Standalone: 1 Execute Inherited: 2 Traceback (most recent call last): File "stack_overflow_class_static_parameter.py", line 52, in <module> my_instance.do_something() ~~~~~~~~~~~~~~~~~~~~~~~~^^ File "stack_overflow_class_static_parameter.py", line 48, in do_something print(f"Execute Nested:{self.Cl_static_parameter_nested.increment()}") ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~^^ File "stack_overflow_class_static_parameter.py", line 38, in increment Cl_static_parameter_nested.c_n_counter += 1 ^^^^^^^^^^^^^^^^^^^^^^^^^^ NameError: name 'Cl_static_parameter_nested' is not defined. Did you mean: 'Cl_static_parameter_standalone'?

Aemyl · Accepted Answer · 2025-04-11 06:19:03Z

You can use the classmethod decorator, which is more appropriate for this situation anyways:

class C: class Nested: counter = 0 @classmethod def increment(cls) -> int: cls.counter += 1 return cls.counter print(C().Nested.increment()) # prints 1

If you are wondering why increment can't find Cl_static_parameter_nested in your example: you would have to write Cl_some_class.Cl_static_parameter_nested to access it from the global namespace.

the inherited version has some wierd quirks anyway. It seems to copy the static var at first call, then use a separate version of it, making it's behaviour weird. Execute Standalone: 1 Execute Inherited: 2 Execute Nested: 1 Execute Standalone: 2 Execute Inherited: 3 Execute Nested: 2

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