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PEP:404
Title:Python 2.8 Un-release Schedule
Version:85ed05373838
Last-Modified:2012-03-05 17:08:36 -0700 (Mon, 05 Mar 2012)
Author:Barry Warsaw <barry at python.org>
Status:Final
Type:Informational
Content-Type:text/x-rst
Created:2011-11-09
Python-Version:2.8

Abstract

This document describes the un-development and un-release schedule for Python 2.8.

Un-release Manager and Crew

Position Name
2.8 Un-release Manager Cardinal Biggles

Un-release Schedule

The current un-schedule is:

  • 2.8 final Never

Official pronouncement

Rule number six: there is no official Python 2.8 release. There never will be an official Python 2.8 release. It is an ex-release. Python 2.7 is the end of the Python 2 line of development.

Upgrade path

The official upgrade path from Python 2.7 is to Python 3.

And Now For Something Completely Different

In all seriousness, there are important reasons why there won't be an official Python 2.8 release, and why you should plan to migrate instead to Python 3.

Python is (as of this writing) more than 20 years old, and Guido and the community have learned a lot in those intervening years. Guido's original concept for Python 3 was to make changes to the language primarily to remove the warts that had grown in the preceding versions. Python 3 was not to be a complete redesign, but instead an evolution of the language, and while maintaining full backward compatibility with Python 2 was explicitly off-the-table, neither were gratuitous changes in syntax or semantics acceptable. In most cases, Python 2 code can be translated fairly easily to Python 3, sometimes entirely mechanically by such tools as 2to3 [1] (there's also a non-trivial subset of the language that will run without modification on both 2.7 and 3.x).

Because maintaining multiple versions of Python is a significant drag on the resources of the Python developers, and because the improvements to the language and libraries embodied in Python 3 are so important, it was decided to end the Python 2 lineage with Python 2.7. Thus, all new development occurs in the Python 3 line of development, and there will never be an official Python 2.8 release. Python 2.7 will however be maintained for longer than the usual period of time.

Here are some highlights of the significant improvements in Python 3. You can read in more detail on the differences [2] between Python 2 and Python 3. There are also many good guides on porting [3] from Python 2 to Python 3.

Strings and bytes

Python 2's basic original strings are called 8-bit strings, and they play a dual role in Python 2 as both ASCII text and as byte sequences. While Python 2 also has a unicode string type, the fundamental ambiguity of the core string type, coupled with Python 2's default behavior of supporting automatic coercion from 8-bit strings to unicode objects when the two are combined, often leads to UnicodeErrors. Python 3's standard string type is Unicode based, and Python 3 adds a dedicated bytes type, but critically, no automatic coercion between bytes and unicode strings is provided. The closest the language gets to implicit coercion are a few text-based APIs that assume a default encoding (usually UTF-8) if no encoding is explicitly stated. Thus, the core interpreter, its I/O libraries, module names, etc. are clear in their distinction between unicode strings and bytes. Python 3's unicode support even extends to the filesystem, so that non-ASCII file names are natively supported.

This string/bytes clarity is often a source of difficulty in transitioning existing code to Python 3, because many third party libraries and applications are themselves ambiguous in this distinction. Once migrated though, most UnicodeErrors can be eliminated.

Numbers

Python 2 has two basic integer types, a native machine-sized int type, and an arbitrary length long type. These have been merged in Python 3 into a single int type analogous to Python 2's long type.

In addition, integer division now produces floating point numbers for non-integer results.

Classes

Python 2 has two core class hierarchies, often called classic classes and new-style classes. The latter allow for such things as inheriting from the builtin basic types, support descriptor based tools like the property builtin and provide a generally more sane and coherent system for dealing with multiple inheritance. Python 3 provided the opportunity to completely drop support for classic classes, so all classes in Python 3 automatically use the new-style semantics (although that's a misnomer now). There is no need to explicitly inherit from object or set the default metatype to enable them (in fact, setting a default metatype at the module level is no longer supported - the default metatype is always object).

The mechanism for explicitly specifying a metaclass has also changed to use a metaclass keyword argument in the class header line rather than a __metaclass__ magic attribute in the class body.

Multiple spellings

There are many cases in Python 2 where multiple spellings of some constructs exist, such as repr() and backticks, or the two inequality operators != and <>. In all cases, Python 3 has chosen exactly one spelling and removed the other (e.g. repr() and != were kept).

Imports

In Python 3, implicit relative imports within packages are no longer available - only absolute imports and explicit relative imports are supported. In addition, star imports (e.g. from x import *) are only permitted in module level code.

Also, some areas of the standard library have been reorganized to make the naming scheme more intuitive. Some rarely used builtins have been relocated to standard library modules.

Iterators and views

Many APIs, which in Python 2 returned concrete lists, in Python 3 now return iterators or lightweight views.