[Python] explain the following attribute lookup

class Test(io.BufferedIOBase):
def __init__(self, f):
self.f = f

def __getattr__(self, name):
print("getattr: searching for: ", name)
#try:
# v = getattr(self.f, name)
#except Exception:
# print(" found nothing!")
# raise
#print(" found: ", v)
#return v
#return 22
raise AttributeError(name)

def __getattribute__(self, name):
print("1.getattribute@self: searching for: ", name, flush=True)
try:
v = super().__getattribute__(name)
except Exception as e:
print(" 1.exception: ", e)
print(" 1.found nothing!", flush=True)
pass
else:
print(" 1.found: ", v, flush=True)
return v
print("2.getattribute@self.f: searching for: ", name, flush=True)
#f = super().__getattribute__("f")
f = object.__getattribute__(self, "f")
try:
v = getattr(f, name)
except Exception as e:
print(" 2.exception: ", e)
print(" 2.found nothing!", flush=True)
raise
else:
print(" 2.found: ", v, flush=True)
return v
print("ERROR")


f1 = open(p, "rb")
f2 = Test(f1)
print("\nTest 01:")
v = f2.closed
print("result: ", v)
print("\nTest 02:")
v = f2.qwer
print("result: ", v)


Test 01:
1.getattribute@self: searching for: closed
1.getattribute@self: searching for: __IOBase_closed
1.exception: 'Test' object has no attribute '__IOBase_closed'
1.found nothing!
2.getattribute@self.f: searching for: __IOBase_closed
2.exception: '_io.BufferedReader' object has no attribute '__IOBase_closed'
2.found nothing!
getattr: searching for: __IOBase_closed
1.found: False
result: False

Test 02:
1.getattribute@self: searching for: qwer
1.exception: 'Test' object has no attribute 'qwer'
1.found nothing!
2.getattribute@self.f: searching for: qwer
2.exception: '_io.BufferedReader' object has no attribute 'qwer'
2.found nothing!
getattr: searching for: qwer
---------------------------------------------------------------------------
AttributeError Traceback (most recent call last)
Cell In[532], line 49
47 print("result: ", v)
48 print("\nTest 02:")
---> 49 v = f2.qwer
50 print("result: ", v)

Cell In[532], line 15, in Test.__getattr__(self, name)
6 print("getattr: searching for: ", name)
7 #try:
8 # v = getattr(self.f, name)
9 #except Exception:
(...)
13 #return v
14 #return 22
---> 15 raise AttributeError(name)

AttributeError: qwer


Following object_getattribute(), this is what I think happens:

1. closed resolves to the non-data property from IOBase.
2. The property is called before the previous __getattribute__ returns, looking up self.__closed, which is actually _IOBase__closed per name-mangling rules.

Now the steps become strange.

1. My __getattribute__ seems to be searching for __IOBase_closed (which doesn't exist), rather than _IOBase__closed. This I can attribute to mismatches between the Python and CPython code.
2. My __getattribute__ fails and raises AttributeError, and then my __getattr__ fails and raises AttributeError. And yet somehow, the value of _IOBase__closed is returned. I can only explain this if Python calls another getattr* function further up the MRO.

So now I'm stumped.

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