What is the difference between old style and new style classes in Python?

Question

What is the difference between old style and new style classes in Python? When should I use one or the other?

Answer 1

Hi there,

New style classes were introduced in Python 2.2 and exist in both Python 2 and Python 3.

Python 2:

Old style classes: do not inherit from object

for example:

class OldStyle:

pass

New style classes: explicitly inherit from object

for example:

class NewStyle(object):

pass

Python 3:

Old style classes no long exist and every class is automatically new style.

If you are working in Python 3, there is no real difference and you'll never need to choose.

If you are working in Python 2, the noticeable differences are:

1. Method Resolution Order - new style classes determine which parent's method to call in multiple inheritance situations.
2. type() behavior - old style classes returned unhelpful information
3. @property, @staticmethod and @classmethod only work correctly with new style classes

So, when should you use one or the other:

1. Python 3 - uses new style automatically
2. Python 2 - always explicitly inherit from object to get new style behavior