class YourClass:
    class_variable = None

    def __init__(self):
        if YourClass.class_variable is None:
            YourClass.class_variable = "default value"
        self.instance_variable = YourClass.class_variable

instance1 = YourClass()
print("instance1>>",instance1.variable)
instance2 = YourClass()
print("instance2>>",instance2.variable)

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