mirror of https://github.com/python/cpython
Issue #13086: Update howto/cporting.rst to discuss "Python 3" instead of "3.0".
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@ -2,27 +2,28 @@
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.. _cporting-howto:
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********************************
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Porting Extension Modules to 3.0
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********************************
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*************************************
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Porting Extension Modules to Python 3
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*************************************
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:author: Benjamin Peterson
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.. topic:: Abstract
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Although changing the C-API was not one of Python 3.0's objectives, the many
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Python level changes made leaving 2.x's API intact impossible. In fact, some
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changes such as :func:`int` and :func:`long` unification are more obvious on
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the C level. This document endeavors to document incompatibilities and how
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they can be worked around.
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Although changing the C-API was not one of Python 3's objectives,
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the many Python-level changes made leaving Python 2's API intact
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impossible. In fact, some changes such as :func:`int` and
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:func:`long` unification are more obvious on the C level. This
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document endeavors to document incompatibilities and how they can
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be worked around.
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Conditional compilation
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=======================
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The easiest way to compile only some code for 3.0 is to check if
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:c:macro:`PY_MAJOR_VERSION` is greater than or equal to 3. ::
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The easiest way to compile only some code for Python 3 is to check
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if :c:macro:`PY_MAJOR_VERSION` is greater than or equal to 3. ::
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#if PY_MAJOR_VERSION >= 3
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#define IS_PY3K
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@ -35,7 +36,7 @@ conditional blocks.
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Changes to Object APIs
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======================
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Python 3.0 merged together some types with similar functions while cleanly
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Python 3 merged together some types with similar functions while cleanly
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separating others.
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@ -43,14 +44,14 @@ str/unicode Unification
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-----------------------
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Python 3.0's :func:`str` (``PyString_*`` functions in C) type is equivalent to
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2.x's :func:`unicode` (``PyUnicode_*``). The old 8-bit string type has become
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:func:`bytes`. Python 2.6 and later provide a compatibility header,
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Python 3's :func:`str` (``PyString_*`` functions in C) type is equivalent to
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Python 2's :func:`unicode` (``PyUnicode_*``). The old 8-bit string type has
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become :func:`bytes`. Python 2.6 and later provide a compatibility header,
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:file:`bytesobject.h`, mapping ``PyBytes`` names to ``PyString`` ones. For best
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compatibility with 3.0, :c:type:`PyUnicode` should be used for textual data and
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compatibility with Python 3, :c:type:`PyUnicode` should be used for textual data and
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:c:type:`PyBytes` for binary data. It's also important to remember that
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:c:type:`PyBytes` and :c:type:`PyUnicode` in 3.0 are not interchangeable like
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:c:type:`PyString` and :c:type:`PyUnicode` are in 2.x. The following example
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:c:type:`PyBytes` and :c:type:`PyUnicode` in Python 3 are not interchangeable like
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:c:type:`PyString` and :c:type:`PyUnicode` are in Python 2. The following example
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shows best practices with regards to :c:type:`PyUnicode`, :c:type:`PyString`,
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and :c:type:`PyBytes`. ::
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@ -94,10 +95,12 @@ and :c:type:`PyBytes`. ::
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long/int Unification
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--------------------
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In Python 3.0, there is only one integer type. It is called :func:`int` on the
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Python level, but actually corresponds to 2.x's :func:`long` type. In the
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C-API, ``PyInt_*`` functions are replaced by their ``PyLong_*`` neighbors. The
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best course of action here is using the ``PyInt_*`` functions aliased to
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Python 3 has only one integer type, :func:`int`. But it actually
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corresponds to Python 2's :func:`long` type--the :func:`int` type
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used in Python 2 was removed. In the C-API, ``PyInt_*`` functions
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are replaced by their ``PyLong_*`` equivalents.
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The best course of action here is using the ``PyInt_*`` functions aliased to
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``PyLong_*`` found in :file:`intobject.h`. The abstract ``PyNumber_*`` APIs
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can also be used in some cases. ::
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@ -120,10 +123,11 @@ can also be used in some cases. ::
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Module initialization and state
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===============================
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Python 3.0 has a revamped extension module initialization system. (See
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:pep:`3121`.) Instead of storing module state in globals, they should be stored
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in an interpreter specific structure. Creating modules that act correctly in
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both 2.x and 3.0 is tricky. The following simple example demonstrates how. ::
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Python 3 has a revamped extension module initialization system. (See
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:pep:`3121`.) Instead of storing module state in globals, they should
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be stored in an interpreter specific structure. Creating modules that
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act correctly in both Python 2 and Python 3 is tricky. The following
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simple example demonstrates how. ::
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#include "Python.h"
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@ -223,15 +227,18 @@ If you're currently using CObjects, and you want to migrate to 3.1 or newer,
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you'll need to switch to Capsules.
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:c:type:`CObject` was deprecated in 3.1 and 2.7 and completely removed in
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Python 3.2. If you only support 2.7, or 3.1 and above, you
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can simply switch to :c:type:`Capsule`. If you need to support 3.0 or
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versions of Python earlier than 2.7 you'll have to support both CObjects
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and Capsules.
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can simply switch to :c:type:`Capsule`. If you need to support Python 3.0,
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or versions of Python earlier than 2.7,
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you'll have to support both CObjects and Capsules.
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(Note that Python 3.0 is no longer supported, and it is not recommended
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for production use.)
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The following example header file :file:`capsulethunk.h` may
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solve the problem for you;
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simply write your code against the :c:type:`Capsule` API, include
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this header file after ``"Python.h"``, and you'll automatically use CObjects
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in Python 3.0 or versions earlier than 2.7.
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solve the problem for you. Simply write your code against the
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:c:type:`Capsule` API and include this header file after
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:file:`Python.h`. Your code will automatically use Capsules
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in versions of Python with Capsules, and switch to CObjects
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when Capsules are unavailable.
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:file:`capsulethunk.h` simulates Capsules using CObjects. However,
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:c:type:`CObject` provides no place to store the capsule's "name". As a
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@ -266,5 +273,5 @@ Other options
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If you are writing a new extension module, you might consider `Cython
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<http://www.cython.org>`_. It translates a Python-like language to C. The
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extension modules it creates are compatible with Python 3.x and 2.x.
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extension modules it creates are compatible with Python 3 and Python 2.
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