[Python-checkins] peps: Update PEP 394 for latest round of python-dev discussions
nick.coghlan
python-checkins at python.org
Thu Feb 16 12:43:04 CET 2012
http://hg.python.org/peps/rev/a15bca819234
changeset: 4056:a15bca819234
user: Nick Coghlan <ncoghlan at gmail.com>
date: Thu Feb 16 21:37:46 2012 +1000
summary:
Update PEP 394 for latest round of python-dev discussions
files:
pep-0394.txt | 94 +++++++++++++++++++++++++--------------
1 files changed, 59 insertions(+), 35 deletions(-)
diff --git a/pep-0394.txt b/pep-0394.txt
--- a/pep-0394.txt
+++ b/pep-0394.txt
@@ -8,7 +8,7 @@
Type: Informational
Content-Type: text/x-rst
Created: 02-Mar-2011
-Post-History: 04-Mar-2011, 20-Jul-2011
+Post-History: 04-Mar-2011, 20-Jul-2011, 16-Feb-2012
Abstract
@@ -39,7 +39,7 @@
Python as either ``python2`` or ``python3``.
* For the time being, it is recommended that ``python`` should refer to
``python2`` (however, some distributions have already chosen otherwise; see
- Notes below).
+ the `Rationale`_ and `Migration Notes`_ below).
* The Python 2.x ``idle``, ``pydoc``, and ``python-config`` commands should
likewise be available as ``idle2``, ``pydoc2``, and ``python2-config``,
with the original commands invoking these versions by default, but possibly
@@ -48,7 +48,7 @@
* In order to tolerate differences across platforms, all new code that needs
to invoke the Python interpreter should not specify ``python``, but rather
should specify either ``python2`` or ``python3`` (or the more specific
- ``python2.x`` and ``python3.x`` versions; see the Notes).
+ ``python2.x`` and ``python3.x`` versions; see the `Migration Notes`_).
This distinction should be made in shebangs, when invoking from a shell
script, when invoking via the system() call, or when invoking in any other
context.
@@ -59,17 +59,15 @@
``sys.executable`` to avoid hardcoded assumptions regarding the
interpreter location remains the preferred approach.
-These recommendations are the outcome of the relevant python-dev discussion in
-March and July 2011 [1][2] (NOTE: More accurately, they will be such once the
-"Draft" status disappears from the PEP header, it has been moved into the
-"Other Informational PEP" section in PEP 0 and this note has been deleted)
+These recommendations are the outcome of the relevant python-dev discussions
+in March and July 2011 ([1]_, [2]_) and February 2012 ([4]_).
Rationale
=========
This is needed as, even though the majority of distributions still alias the
-``python`` command to Python 2, some now alias it to Python 3. Some of
+``python`` command to Python 2, some now alias it to Python 3 ([5]_). Some of
the former also do not provide a ``python2`` command; hence, there is
currently no way for Python 2 code (or any code that invokes the Python 2
interpreter directly rather than via ``sys.executable``) to reliably run on
@@ -80,8 +78,14 @@
minimal additional work required on the part of distribution maintainers.
-Notes
-=====
+Migration Notes
+===============
+
+This section does not contain any official recommendations from the core
+CPython developers. It's merely a collection of notes regarding various
+aspects of migrating to Python 3 as the default version of Python for a
+system. They will hopefully be helpful to any distributions considering
+making such a change.
* Distributions that only include ``python3`` in their base install (i.e.
they do not provide ``python2`` by default) along with those that are
@@ -107,7 +111,7 @@
rather being provided as a separate binary file.
* It is suggested that even distribution-specific packages follow the
``python2``/``python3`` convention, even in code that is not intended to
- operate on other distributions. This will prevent problems if the
+ operate on other distributions. This will reduce problems if the
distribution later decides to change the version of the Python interpreter
that the ``python`` command invokes, or if a sysadmin installs a custom
``python`` command with a different major version than the distribution
@@ -128,8 +132,10 @@
continue to use the ``python3`` convention rather that just ``python``. This
will ease transition in the event that yet another major version of Python
is released.
-* If these conventions are adhered to, it will be the case that the ``python``
- command is only executed in an interactive manner.
+* If these conventions are adhered to, it will become the case that the
+ ``python`` command is only executed in an interactive manner as a user
+ convenience, or to run scripts that are source compatible with both Python
+ 2 and Python 3.
Backwards Compatibility
@@ -147,25 +153,38 @@
Application to the CPython Reference Interpreter
================================================
-While technically a new feature, the ``make install`` command in the 2.7
-version of CPython will be adjusted to create the ``python2.7``, ``idle2.7``,
-``pydoc2.7``, and ``python2.7-config`` binaries, with ``python2``, ``idle2``,
-``pydoc2``, and ``python2-config`` as hard links to the respective binaries,
-and ``python``, ``idle``, ``pydoc``, and ``python-config`` as symbolic links
-to the respective hard links. This feature will first appear in CPython
-2.7.3.
+While technically a new feature, the ``make install`` and ``make bininstall``
+command in the 2.7 version of CPython will be adjusted to create the
+following chains of symbolic links in the relevant ``bin`` directory (the
+final item listed in the chain is the actual installed binary, preceding
+items are relative symbolic links)::
-The ``make install`` command in the CPython 3.x series will similarly install
-the ``python3.x``, ``idle3.x``, ``pydoc3.x``, and ``python3.x-config``
-binaries (with appropriate ``x``), and ``python3``, ``idle3``, ``pydoc3``,
-and ``python3-config`` as hard links. This feature will first appear in
-CPython 3.3.
+ python -> python2 -> python2.7
+ python-config -> python2-config -> python2.7-config
Similar adjustments will be made to the Mac OS X binary installer.
-As implementation of these features in the default installers does not alter
-the recommendations in this PEP, the implementation progress is managed on the
-tracker as issue #12627 [3].
+This feature will first appear in the default installation process in
+CPython 2.7.3.
+
+The installation commands in the CPython 3.x series already create the
+appropriate symlinks. For example, CPython 3.2 creates::
+
+ python3 -> python3.2
+ idle3 -> idle3.2
+ pydoc3 -> pydoc3.2
+ python3-config -> python3.2-config
+
+And CPython 3.3 will create::
+
+ python3 -> python3.3
+ idle3 -> idle3.3
+ pydoc3 -> pydoc3.3
+ python3-config -> python3.3-config
+ pysetup3 -> pysetup3.3
+
+The implementation progress of these features in the default installers is
+managed on the tracker as issue #12627 ([3]_).
Impact on PYTHON* Environment Variables
@@ -192,16 +211,21 @@
References
==========
-[1] Support the /usr/bin/python2 symlink upstream (with bonus grammar class!)
- (http://mail.python.org/pipermail/python-dev/2011-March/108491.html)
+.. [1] Support the /usr/bin/python2 symlink upstream (with bonus grammar class!)
+ (http://mail.python.org/pipermail/python-dev/2011-March/108491.html)
-[2] Rebooting PEP 394 (aka Support the /usr/bin/python2 symlink upstream)
- (http://mail.python.org/pipermail/python-dev/2011-July/112322.html)
+.. [2] Rebooting \PEP 394 (aka Support the /usr/bin/python2 symlink upstream)
+ (http://mail.python.org/pipermail/python-dev/2011-July/112322.html)
-[3] Implement PEP 394 in the CPython Makefile
- (http://bugs.python.org/issue12627)
+.. [3] Implement \PEP 394 in the CPython Makefile
+ (http://bugs.python.org/issue12627)
+
+.. [4] \PEP 394 request for pronouncement (python2 symlink in \*nix systems)
+ (http://mail.python.org/pipermail/python-dev/2012-February/116435.html)
+
+.. [5] Arch Linux announcement that their "python" link now refers Python 3
+ (https://www.archlinux.org/news/python-is-now-python-3/)
Copyright
===========
This document has been placed in the public domain.
-
--
Repository URL: http://hg.python.org/peps
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