Implementing abstract methods in Python 3

Question

I am just trying to practice coding an abstract method in Python and i have the following code for it:

import abc
class test(abc.ABC):
 @abc.abstractmethod
 def first(self,name):
 """This is to be implemented"""
class Extendtest(test):
 def __init__(self,name):
 self.name = name
 def first(self):
 print ("Changing name!")
 self.name = "Shaayan"
 def second(self,value):
 print ("Adding second argument!")
 self.value = value
e = Extendtest("Subhayan")
print (e.name) 
e.first()
print (e.name)

I intentionally changed the signature of the first method in the implementation of the abstract method.

But if i change the signature Python is not giving any error and is going through as expected.

Is there no way in Python by which i can force strict abstraction ?

• Daniel: In Python abstract methods are not necessary. Just use duck-typing.

Answer 1

This is not a new question asked about python and a short answer:

No, it is not possible. The easiest way is either to reuse a custom library like zope or implement this behavior by your own.

There was a proposal on ABC to check arguments and here is what Guido answers on this:

That is not a new idea. So far I have always rejected it because I worry about both false positives and false negatives. Trying to enforce that the method behaves as it should (or even its return type) is hopeless; there can be a variety of reasons to modify the argument list while still conforming to (the intent of) the interface. I also worry that it will slow everything down.

That said, if you want to provide a standard mechanism that can optionally be turned on to check argument conformance, e.g. by using a class or method decorator on the subclass, I would be fine with that (as long as it runs purely at class-definition time; it shouldn't slow down class instantiation or method calls). It will probably even find some bugs. It will also surely have to be tuned to avoid certain classes false positives.

reference to the thread