Old-Style vs. New-Style Classes in Python: What's the Difference?

New-Style vs. Old-Style Classes in Python

Old-style classes were prevalent in Python up until version 2.1, whereas new-style classes were introduced with Python 2.2. The primary distinction between the two revolves around the concept of types versus classes.

Old-Style Classes:

Old-style classes are not directly linked to the concept of types. Instances of old-style classes are all implemented using a single built-in type known as "instance." This means that x.__class__ and type(x) may not always return the same value for an old-style class instance.

New-Style Classes:

New-style classes, on the other hand, unify the concepts of class and type. A new-style class defines a user-defined type, and instances of new-style classes are treated as objects of that type. Typically, type(x) and x.__class__ return the same value for new-style class instances, unless overridden.

Key Differences and Benefits of New-Style Classes:

• Unified object model with a full meta-model.
• Ability to subclass most built-in types.
• Introduction of "descriptors" for computed properties.
• More consistent and intuitive behavior in inheritance scenarios.

When to Use Old-Style vs. New-Style Classes:

For backward compatibility reasons, classes in Python 2.x are old-style by default. To create a new-style class, explicitly specify a new-style class as a parent class.

In Python 3, all classes are new-style. Therefore, there is no need to distinguish between the two styles.

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