[Python-checkins] peps: And now for something completely different.

[barry.warsaw]

http://hg.python.org/peps/rev/804b6389c282
changeset:   3987:804b6389c282
user:        Barry Warsaw <barry at python.org>
date:        Sun Nov 13 16:33:25 2011 -0500
summary:
  And now for something completely different.

files:
  pep-0404.txt |  102 ++++++++++++++++++++++++++++++++++++++-
  1 files changed, 101 insertions(+), 1 deletions(-)


diff --git a/pep-0404.txt b/pep-0404.txt
--- a/pep-0404.txt
+++ b/pep-0404.txt
@@ -39,7 +39,8 @@
 ======================
 
 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.
+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
@@ -48,12 +49,111 @@
 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) nearly 20 years old, and Guido and the
+community has 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 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`_.
+
+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_ between Python 2 and
+Python 3.  There are also many good guides on porting_ from Python 2
+to Python 3.
+
+
+Strings and bytes
+-----------------
+
+Python 2's basic original string type are called 8-bit strings, and
+they play a dual role in Python 2 as both ASCII text and as byte
+arrays.  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 unicodes when the two are combined, often leads to `UnicodeError`s.
+Python 3's standard string type is a unicode, and Python 3 adds a
+bytes type, but critically, no automatic coercion between bytes and
+unicodes is provided.  Thus, the core interpreter, its I/O libraries,
+module names, etc. are clear in their distinction between unicode
+strings and bytes.  This 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 `UnicodeError`s 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.
+
+
+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, star imports (e.g. ``from x import *``) are only
+premitted in module level code.  Also, only absolute imports are
+supported.
+
+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*.
+
+
 Copyright
 =========
 
 This document has been placed in the public domain.
 
 
+.. _`2to3`: http://docs.python.org/library/2to3.html
+.. _differences: http://docs.python.org/release/3.0.1/whatsnew/3.0.html
+.. _porting: http://python3porting.com/
+
+
 
 ..
   Local Variables:

-- 
Repository URL: http://hg.python.org/peps