[Python] Inherit a class with class variables

If there are multiple classes that inherit from the parent class that has class variables Note that the behavior when the child class accesses the class variable was suspicious.

Conclusion (?):

--Mutable class variables are likely to be shared even in the inherited child class. --Overwrite the same variable in the child class if you want to manage them separately

Symptoms

#Parent class
class AbstClass:
    class_number = 0
    dict_number = {'class': 0}

#Child class 1
class Class1(AbstClass):
    def __init__(self):
        self.class_number = 1
        self.dict_number['class'] = 1

#Child class 2
class Class2(AbstClass):
    def __init__(self):
        self.class_number = 2
        self.dict_number['class'] = 2

obj1 = Class1()
print(obj1.class_number, obj1.dict_number['class']) # 1,1 ← Understand
obj2 = Class2()
print(obj2.class_number, obj2.dict_number['class']) # 2,2 ← Understand
print(obj1.class_number, obj1.dict_number['class']) # 1, 2 ←!?

It is easy to understand if "two child classes are accessing the class variables of the same parent class", In the above example

--class_number is managed separately by two classes --dict_number is shared by two classes → Overwrites dict_numer rewritten in Class1 when Class2 () is done

It has become.

Cause hypothesis

Is mutable / immutable involved? I guess. In other words

--mutable class variables (dict_number above): shared by child classes --immutable class variables (class_number above): managed separately in child classes

In fact, if you define a tuple of class_number_tuple = (0,) in AbstClass, The same behavior as class_number was confirmed. (* Int is immutable. Reference: [GAMMASOFT: Python built-in data type classification table (mutable, etc.)] (https://gammasoft.jp/blog/python-built-in-types/)）

Countermeasures

Redefine class variables in child classes:

class Class1(AbstClass):
    class_number = 0
    dict_kv = {'class': 0}

class Class2(AbstClass):
    class_number = 0
    dict_kv = {'class': 0}

And, in each instance, the class variable of each class is prioritized = it will be managed separately.

However, if you want, I want you to automatically raise an exception as a language.

――In fact, when I put a list in the key of the dictionary, I get angry with unhashable --If it is possible to specify "class variables to be shared" and "class variables to be overwritten by child classes" like @abstractmethod of ABC ...

As a current measure,

--Do not define class variables in abstract classes that are supposed to be inherited (as mentioned above, it is safer to redefine in child classes, so it is simply a waste of lines) --Use delegation instead of inheritance when you need to access class variables of other classes (ideal) --Read the source code of the inherited class even at the beginning (reality)

Is it about ... I would appreciate it if you could tell me any good measures.