Python 2.2: What's New, Release History & Support Lifecycle

What Is New in Python 2.2

Python 2.2 was one of the most fundamental Python releases -- it unified the old-style and new-style object system, introduced descriptors, properties, and slots, and brought generators into the language. These changes laid the groundwork for everything Python's object model is today.

The Most Important Python 2.2 Changes

New-Style Classes and the Unified Object Model

Before Python 2.2, there were two class flavors: "old-style" (classic) classes defined with class Foo: and the built-in types like int, list, dict. They were separate hierarchies with different behaviors. Python 2.2 unified them -- new-style classes inherit from object (explicitly or via a built-in type) and have consistent semantics for __init__, __new__, descriptors, and MRO.

# Old-style class (Python 2 only, deprecated)
class OldFoo:
    pass

# New-style class (Python 2.2+, only kind in Python 3)
class NewFoo(object):
    pass

# In Python 3, all classes are new-style automatically
class Foo:  # implicitly inherits from object
    pass

Descriptors and property() (PEP 252)

Descriptors are objects that define __get__, __set__, or __delete__ -- they control what happens when you access an attribute on a class or instance. The property() built-in uses descriptors to create managed attributes with getter, setter, and deleter methods.

class Temperature:
    def __init__(self, celsius=0):
        self._celsius = celsius

    @property
    def celsius(self):
        return self._celsius

    @celsius.setter
    def celsius(self, value):
        if value < -273.15:
            raise ValueError("Below absolute zero")
        self._celsius = value

    @property
    def fahrenheit(self):
        return self._celsius * 9/5 + 32

Generators (PEP 255)

Functions containing yield become generator functions. Calling one returns a generator object that produces values lazily. This was the building block for Python's async and iteration story in later versions.

def fibonacci():
    a, b = 0, 1
    while True:
        yield a
        a, b = b, a + b

gen = fibonacci()
first_10 = [next(gen) for _ in range(10)]
# [0, 1, 1, 2, 3, 5, 8, 13, 21, 34]