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pythonpython-3.xabstract-class

Abstract Method override in Python


If I create an abstract class in python using abc with an abstractmethod as follows and create a concrete class which doesn't use def to override the abstractmethod but instead attempt to set the attribute in the init function, it continues to throw the error that we can't instantiate an abstract class. I found out that I can get around this problem by creating a dummy of the abstractmethod. Is this the recommended way?

from abc import ABC, abstractmethod

class MyAbstract(ABC):
  def __init__(self):
    pass

  @abstractmethod
  def hi(self):
    pass

class Concrete(MyAbstract):
  def __init__(self, selector):
     if selector:
       self.hi = self.hi_a
     else:
       self.hi = self.hi_b

  def hi(self):
    '''
    Is it possible to not have to create this function?
    '''
    pass

  def hi_a(self):
     print('a')

  def hi_b(self):
     print('b')

Solution

  • class Concrete(MyAbstract):
        hi = None
    
        ...
    

    This suffices to allow instantiation. The class simply mustn't have any attribute decorated with @abstractXXX at time of instantiation. Replacing the inherited hi with any other hi is enough to achieve that.