Is it OK to extend both old and new style classes?

Question

When I extended some tool generated classes, I didn't realize that they are old style classes until I tried to use super(). The super() doesn't work with old style classes, so I got this error:

TypeError: super() argument 1 must be type, not classobj

E.g., try this snippet:

>>> class A:
...     def greet(self):
...         print "A says hi"
...
>>> class B(A):
...     def greet(self):
...         print "B says hi"
...
>>> super(B, B()).greet()
Traceback (most recent call last):
  File "<stdin>", line 1, in <module>
TypeError: super() argument 1 must be type, not classobj

I was just curious what would happen if I extended B from object as well to make it a new style class, and it seemed to make super() work.

>>> class B(A, object):
...     def greet(self):
...         print "B says hi"
...
>>> super(B, B()).greet()
A says hi

Is this an appropriate workaround or will I have some unwanted consequences later?

Answer 1

New-style classes have been recommended practice in Python since they were introduced in Python 2.2. In Python 3.x, only new-style classes are available. Therefore, I recommend you switch your classes to new-style.

I am not aware of any real problems you might have from this. For the most part, new-style classes simply bring new features, such as super() actually working. If you have code that relies on the semantics of old-style classes in tricky ways, that code would of course break. (The only example that comes to mind is the famous Borg pattern by the famous Alex Martelli.)

Here is a link to the Python reference manual for a discussion of new style classes vs. old-style ("classic") classes. And here is a link to the classic essay where Guido van Rossum explains why new-style classes were introduced.

I use only new-style classes in my code and I encourage you to do the same.