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List:       python-list
Subject:    Instantiating abstract classes
From:       Peter Otten <__peter__ () web ! de>
Date:       2021-05-21 18:00:23
Message-ID: s88sfo$13je$1 () ciao ! gmane ! io
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Usually an abstract class cannot be instantiated:

 >>> from abc import ABCMeta, abstractmethod
 >>> from fractions import Fraction
 >>> class A(Fraction, metaclass=ABCMeta):
	@abstractmethod
	def frobnicate(self): pass

	
 >>> A()
Traceback (most recent call last):
   File "<pyshell#287>", line 1, in <module>
     A()
   File "C:\Program Files\Python39-32\lib\fractions.py", line 93, in __new__
     self = super(Fraction, cls).__new__(cls)
TypeError: Can't instantiate abstract class A with abstract method 
frobnicate


However, if I derive from a builtin class that mechanism doesn't work:

 >>> class A(int, metaclass=ABCMeta):
	@abstractmethod
	def frobnicate(self): pass

	
 >>> A()
0

Is this a bug, or an implementation accident, or the expected behavior?

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