Sebastian Sebastian - 1 month ago 20
Python Question

python @abstractmethod decorator

I have read python docs about abstract base classes:

From here:


abc.abstractmethod(function)

A decorator indicating abstract methods.

Using this decorator requires that the class’s metaclass is
ABCMeta
or
is derived from it. A class that has a metaclass derived from
ABCMeta

cannot be instantiated unless all of its abstract methods and
properties are overridden.


And here


You can apply the
@abstractmethod
decorator to methods such as draw()
that must be implemented; Python will then raise an exception for
classes that don’t define the method. Note that the exception is only
raised when you actually try to create an instance of a subclass
lacking the method.


I've used this code to test that out:

import abc

class AbstractClass(object):
__metaclass__ = abc.ABCMeta

@abc.abstractmethod
def abstractMethod(self):
return

class ConcreteClass(AbstractClass):
def __init__(self):
self.me = "me"

c = ConcreteClass()
c.abstractMethod()


The code goes fine, so I don't get it. If I type
c.abstractMethod
I get:

<bound method ConcreteClass.abstractMethod of <__main__.ConcreteClass object at 0x7f694da1c3d0>>


What I'm missing here?
ConcreteClass
must implement the abstract methods, but I get no exception.

Answer

Are you using python3 to run that code ? if yes you should know that declaring metaclass in python 3 have changes you should do it like this instead:

import abc

class AbstractClass(metaclass=abc.ABCMeta):

  @abc.abstractmethod
  def abstractMethod(self):
      return