Issue #13086: Update howto/cporting.rst to discuss "Python 3" instead of "3.0".

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Larry Hastings 2012-02-28 15:17:23 -08:00
parent a6bdfd1fa9
commit 0555cde98d
1 changed files with 40 additions and 33 deletions

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@ -2,27 +2,28 @@
.. _cporting-howto:
********************************
Porting Extension Modules to 3.0
********************************
*************************************
Porting Extension Modules to Python 3
*************************************
:author: Benjamin Peterson
.. topic:: Abstract
Although changing the C-API was not one of Python 3.0's objectives, the many
Python level changes made leaving 2.x's API intact impossible. In fact, some
changes such as :func:`int` and :func:`long` unification are more obvious on
the C level. This document endeavors to document incompatibilities and how
they can be worked around.
Although changing the C-API was not one of Python 3's objectives,
the many Python-level changes made leaving Python 2's API intact
impossible. In fact, some changes such as :func:`int` and
:func:`long` unification are more obvious on the C level. This
document endeavors to document incompatibilities and how they can
be worked around.
Conditional compilation
=======================
The easiest way to compile only some code for 3.0 is to check if
:c:macro:`PY_MAJOR_VERSION` is greater than or equal to 3. ::
The easiest way to compile only some code for Python 3 is to check
if :c:macro:`PY_MAJOR_VERSION` is greater than or equal to 3. ::
#if PY_MAJOR_VERSION >= 3
#define IS_PY3K
@ -35,7 +36,7 @@ conditional blocks.
Changes to Object APIs
======================
Python 3.0 merged together some types with similar functions while cleanly
Python 3 merged together some types with similar functions while cleanly
separating others.
@ -43,14 +44,14 @@ str/unicode Unification
-----------------------
Python 3.0's :func:`str` (``PyString_*`` functions in C) type is equivalent to
2.x's :func:`unicode` (``PyUnicode_*``). The old 8-bit string type has become
:func:`bytes`. Python 2.6 and later provide a compatibility header,
Python 3's :func:`str` (``PyString_*`` functions in C) type is equivalent to
Python 2's :func:`unicode` (``PyUnicode_*``). The old 8-bit string type has
become :func:`bytes`. Python 2.6 and later provide a compatibility header,
:file:`bytesobject.h`, mapping ``PyBytes`` names to ``PyString`` ones. For best
compatibility with 3.0, :c:type:`PyUnicode` should be used for textual data and
compatibility with Python 3, :c:type:`PyUnicode` should be used for textual data and
:c:type:`PyBytes` for binary data. It's also important to remember that
:c:type:`PyBytes` and :c:type:`PyUnicode` in 3.0 are not interchangeable like
:c:type:`PyString` and :c:type:`PyUnicode` are in 2.x. The following example
:c:type:`PyBytes` and :c:type:`PyUnicode` in Python 3 are not interchangeable like
:c:type:`PyString` and :c:type:`PyUnicode` are in Python 2. The following example
shows best practices with regards to :c:type:`PyUnicode`, :c:type:`PyString`,
and :c:type:`PyBytes`. ::
@ -94,10 +95,12 @@ and :c:type:`PyBytes`. ::
long/int Unification
--------------------
In Python 3.0, there is only one integer type. It is called :func:`int` on the
Python level, but actually corresponds to 2.x's :func:`long` type. In the
C-API, ``PyInt_*`` functions are replaced by their ``PyLong_*`` neighbors. The
best course of action here is using the ``PyInt_*`` functions aliased to
Python 3 has only one integer type, :func:`int`. But it actually
corresponds to Python 2's :func:`long` type--the :func:`int` type
used in Python 2 was removed. In the C-API, ``PyInt_*`` functions
are replaced by their ``PyLong_*`` equivalents.
The best course of action here is using the ``PyInt_*`` functions aliased to
``PyLong_*`` found in :file:`intobject.h`. The abstract ``PyNumber_*`` APIs
can also be used in some cases. ::
@ -120,10 +123,11 @@ can also be used in some cases. ::
Module initialization and state
===============================
Python 3.0 has a revamped extension module initialization system. (See
:pep:`3121`.) Instead of storing module state in globals, they should be stored
in an interpreter specific structure. Creating modules that act correctly in
both 2.x and 3.0 is tricky. The following simple example demonstrates how. ::
Python 3 has a revamped extension module initialization system. (See
:pep:`3121`.) Instead of storing module state in globals, they should
be stored in an interpreter specific structure. Creating modules that
act correctly in both Python 2 and Python 3 is tricky. The following
simple example demonstrates how. ::
#include "Python.h"
@ -223,15 +227,18 @@ If you're currently using CObjects, and you want to migrate to 3.1 or newer,
you'll need to switch to Capsules.
:c:type:`CObject` was deprecated in 3.1 and 2.7 and completely removed in
Python 3.2. If you only support 2.7, or 3.1 and above, you
can simply switch to :c:type:`Capsule`. If you need to support 3.0 or
versions of Python earlier than 2.7 you'll have to support both CObjects
and Capsules.
can simply switch to :c:type:`Capsule`. If you need to support Python 3.0,
or versions of Python earlier than 2.7,
you'll have to support both CObjects and Capsules.
(Note that Python 3.0 is no longer supported, and it is not recommended
for production use.)
The following example header file :file:`capsulethunk.h` may
solve the problem for you;
simply write your code against the :c:type:`Capsule` API, include
this header file after ``"Python.h"``, and you'll automatically use CObjects
in Python 3.0 or versions earlier than 2.7.
solve the problem for you. Simply write your code against the
:c:type:`Capsule` API and include this header file after
:file:`Python.h`. Your code will automatically use Capsules
in versions of Python with Capsules, and switch to CObjects
when Capsules are unavailable.
:file:`capsulethunk.h` simulates Capsules using CObjects. However,
:c:type:`CObject` provides no place to store the capsule's "name". As a
@ -266,5 +273,5 @@ Other options
If you are writing a new extension module, you might consider `Cython
<http://www.cython.org>`_. It translates a Python-like language to C. The
extension modules it creates are compatible with Python 3.x and 2.x.
extension modules it creates are compatible with Python 3 and Python 2.