2.2. New and Old Style Class

• Old Style classes - Not existing in Python 3

• In Python 3 class will always produce new style class

• The major motivation for introducing new-style classes is to provide a unified object model with a full meta-model

• https://docs.python.org/dev/tutorial/classes.html

2.2.1. Old Style classes

• Not existing in Python 3

• Don't inherit from object

• In Python 3, there are no old-style classes, and this code will produce new style class

2.2.2. New Style Class

• Introduced in Python 2.2

• In Python 3 this is the only way

• Inherit from object or from another new style class

• Ability to subclass most built-in types

• super() added

• MRO changed

• descriptors added

• new style class objects cannot be raised unless derived from Exception

• __slots__ added

2.2.3. Definition

• Old style classes are only in Python 2

• New style classes works in Python 2 (when inherit from object)

• In Python 3 all classes always inherit from object, hence they are new style classes

# Python 2.x
# old style class
# inherits from type

class MyClass:
    pass

# Python > 2.2
# new style class
# inherits from object

class MyClass(object):
    pass

# Python 3.x
# meta class
# inherits from type

class MyClass(metaclass=type):
    pass

# Python 3.x
# new style class
# inherits from object

class MyClass:
    pass

# Python 3.x
# new style class
# inherits from object

class MyClass(object):
    pass