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class A:
	x = 1
	def __getattr__(self,name):
		print("__getattr__ of A")
	def __getattribute__(self,name):
		print("__getattribute__ of A")
		return super().__getattribute__(name)

class B(A):
	x = 2
	def __getattr__(self,name):
		print("__getattr__ of B")
	def __getattribute__(self,name):
		print("__getattribute__ of B")
		a = A()
		return a.__getattribute__(name)
b = B()
print(b.x)

I want to ask Why A will be printed twice.I have tried debug ,but after that I am more puzzled.Thanks.

the __getattribute__ method is called twice on line 16: first implicitly to get the __getattribute__ method itself, and then explicitly by your code.

(Jul-25-2018, 11:19 AM)stranac Wrote: [ -> ]the __getattribute__ method is called twice on line 16: first implicitly to get the __getattribute__ method itself, and then explicitly by your code.

Thank you.But I have an another problem,

class B(A):
        x = 2
        def __getattr__(self,name):
                print("__getattr__ of B")
        def __getattribute__(self,name):
                print("__getattribute__ of B")
                return object().__getattribute__(name)

        
b = B()
b.x

why the output is:
__getattribute__ of B
__getattr__ of B

In this case, __getattribute__ gets called first, and raises an AttributeError, because x is an attribute of the class, not the instance.
When this happens, __getattr__ gets called to get the class attribute.

You should read https://docs.python.org/3/reference/datamodel.html to get a better understanding of how all of this stuff works.