mirror of
https://github.com/python/cpython.git
synced 2024-11-24 02:15:30 +08:00
bpo-24937: Replace the extension module porting HOWTO by links to external projects (GH-9317)
This commit is contained in:
Petr Viktorin
GitHub
parent
558c49bcf3
commit
2d3ff2b5ea
@ -6,252 +6,21 @@
|
||||
Porting Extension Modules to Python 3
|
||||
*************************************
|
||||
|
||||
:author: Benjamin Peterson
|
||||
We recommend the following resources for porting extension modules to Python 3:
|
||||
|
||||
* The `Migrating C extensions`_ chapter from
|
||||
*Supporting Python 3: An in-depth guide*, a book on moving from Python 2
|
||||
to Python 3 in general, guides the reader through porting an extension
|
||||
module.
|
||||
* The `Porting guide`_ from the *py3c* project provides opinionated
|
||||
suggestions with supporting code.
|
||||
* The `Cython`_ and `CFFI`_ libraries offer abstractions over
|
||||
Python's C API.
|
||||
Extensions generally need to be re-written to use one of them,
|
||||
but the library then handles differences between various Python
|
||||
versions and implementations.
|
||||
|
||||
.. topic:: Abstract
|
||||
|
||||
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 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
|
||||
#endif
|
||||
|
||||
API functions that are not present can be aliased to their equivalents within
|
||||
conditional blocks.
|
||||
|
||||
|
||||
Changes to Object APIs
|
||||
======================
|
||||
|
||||
Python 3 merged together some types with similar functions while cleanly
|
||||
separating others.
|
||||
|
||||
|
||||
str/unicode Unification
|
||||
-----------------------
|
||||
|
||||
Python 3's :func:`str` type is equivalent to Python 2's :func:`unicode`; the C
|
||||
functions are called ``PyUnicode_*`` for both. The old 8-bit string type has become
|
||||
:func:`bytes`, with C functions called ``PyBytes_*``. Python 2.6 and later provide a compatibility header,
|
||||
:file:`bytesobject.h`, mapping ``PyBytes`` names to ``PyString`` ones. For best
|
||||
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 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`. ::
|
||||
|
||||
#include "stdlib.h"
|
||||
#include "Python.h"
|
||||
#include "bytesobject.h"
|
||||
|
||||
/* text example */
|
||||
static PyObject *
|
||||
say_hello(PyObject *self, PyObject *args) {
|
||||
PyObject *name, *result;
|
||||
|
||||
if (!PyArg_ParseTuple(args, "U:say_hello", &name))
|
||||
return NULL;
|
||||
|
||||
result = PyUnicode_FromFormat("Hello, %S!", name);
|
||||
return result;
|
||||
}
|
||||
|
||||
/* just a forward */
|
||||
static char * do_encode(PyObject *);
|
||||
|
||||
/* bytes example */
|
||||
static PyObject *
|
||||
encode_object(PyObject *self, PyObject *args) {
|
||||
char *encoded;
|
||||
PyObject *result, *myobj;
|
||||
|
||||
if (!PyArg_ParseTuple(args, "O:encode_object", &myobj))
|
||||
return NULL;
|
||||
|
||||
encoded = do_encode(myobj);
|
||||
if (encoded == NULL)
|
||||
return NULL;
|
||||
result = PyBytes_FromString(encoded);
|
||||
free(encoded);
|
||||
return result;
|
||||
}
|
||||
|
||||
|
||||
long/int Unification
|
||||
--------------------
|
||||
|
||||
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.
|
||||
|
||||
|
||||
Module initialization and state
|
||||
===============================
|
||||
|
||||
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"
|
||||
|
||||
struct module_state {
|
||||
PyObject *error;
|
||||
};
|
||||
|
||||
#if PY_MAJOR_VERSION >= 3
|
||||
#define GETSTATE(m) ((struct module_state*)PyModule_GetState(m))
|
||||
#else
|
||||
#define GETSTATE(m) (&_state)
|
||||
static struct module_state _state;
|
||||
#endif
|
||||
|
||||
static PyObject *
|
||||
error_out(PyObject *m) {
|
||||
struct module_state *st = GETSTATE(m);
|
||||
PyErr_SetString(st->error, "something bad happened");
|
||||
return NULL;
|
||||
}
|
||||
|
||||
static PyMethodDef myextension_methods[] = {
|
||||
{"error_out", (PyCFunction)error_out, METH_NOARGS, NULL},
|
||||
{NULL, NULL}
|
||||
};
|
||||
|
||||
#if PY_MAJOR_VERSION >= 3
|
||||
|
||||
static int myextension_traverse(PyObject *m, visitproc visit, void *arg) {
|
||||
Py_VISIT(GETSTATE(m)->error);
|
||||
return 0;
|
||||
}
|
||||
|
||||
static int myextension_clear(PyObject *m) {
|
||||
Py_CLEAR(GETSTATE(m)->error);
|
||||
return 0;
|
||||
}
|
||||
|
||||
|
||||
static struct PyModuleDef moduledef = {
|
||||
PyModuleDef_HEAD_INIT,
|
||||
"myextension",
|
||||
NULL,
|
||||
sizeof(struct module_state),
|
||||
myextension_methods,
|
||||
NULL,
|
||||
myextension_traverse,
|
||||
myextension_clear,
|
||||
NULL
|
||||
};
|
||||
|
||||
#define INITERROR return NULL
|
||||
|
||||
PyMODINIT_FUNC
|
||||
PyInit_myextension(void)
|
||||
|
||||
#else
|
||||
#define INITERROR return
|
||||
|
||||
void
|
||||
initmyextension(void)
|
||||
#endif
|
||||
{
|
||||
#if PY_MAJOR_VERSION >= 3
|
||||
PyObject *module = PyModule_Create(&moduledef);
|
||||
#else
|
||||
PyObject *module = Py_InitModule("myextension", myextension_methods);
|
||||
#endif
|
||||
|
||||
if (module == NULL)
|
||||
INITERROR;
|
||||
struct module_state *st = GETSTATE(module);
|
||||
|
||||
st->error = PyErr_NewException("myextension.Error", NULL, NULL);
|
||||
if (st->error == NULL) {
|
||||
Py_DECREF(module);
|
||||
INITERROR;
|
||||
}
|
||||
|
||||
#if PY_MAJOR_VERSION >= 3
|
||||
return module;
|
||||
#endif
|
||||
}
|
||||
|
||||
|
||||
CObject replaced with Capsule
|
||||
=============================
|
||||
|
||||
The :c:type:`Capsule` object was introduced in Python 3.1 and 2.7 to replace
|
||||
:c:type:`CObject`. CObjects were useful,
|
||||
but the :c:type:`CObject` API was problematic: it didn't permit distinguishing
|
||||
between valid CObjects, which allowed mismatched CObjects to crash the
|
||||
interpreter, and some of its APIs relied on undefined behavior in C.
|
||||
(For further reading on the rationale behind Capsules, please see :issue:`5630`.)
|
||||
|
||||
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 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 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
|
||||
result the simulated :c:type:`Capsule` objects created by :file:`capsulethunk.h`
|
||||
behave slightly differently from real Capsules. Specifically:
|
||||
|
||||
* The name parameter passed in to :c:func:`PyCapsule_New` is ignored.
|
||||
|
||||
* The name parameter passed in to :c:func:`PyCapsule_IsValid` and
|
||||
:c:func:`PyCapsule_GetPointer` is ignored, and no error checking
|
||||
of the name is performed.
|
||||
|
||||
* :c:func:`PyCapsule_GetName` always returns NULL.
|
||||
|
||||
* :c:func:`PyCapsule_SetName` always raises an exception and
|
||||
returns failure. (Since there's no way to store a name
|
||||
in a CObject, noisy failure of :c:func:`PyCapsule_SetName`
|
||||
was deemed preferable to silent failure here. If this is
|
||||
inconvenient, feel free to modify your local
|
||||
copy as you see fit.)
|
||||
|
||||
You can find :file:`capsulethunk.h` in the Python source distribution
|
||||
as :source:`Doc/includes/capsulethunk.h`. We also include it here for
|
||||
your convenience:
|
||||
|
||||
.. literalinclude:: ../includes/capsulethunk.h
|
||||
|
||||
|
||||
|
||||
Other options
|
||||
=============
|
||||
|
||||
If you are writing a new extension module, you might consider `Cython
|
||||
<http://cython.org/>`_. It translates a Python-like language to C. The
|
||||
extension modules it creates are compatible with Python 3 and Python 2.
|
||||
|
||||
.. _Migrating C extensions: http://python3porting.com/cextensions.html
|
||||
.. _Porting guide: https://py3c.readthedocs.io/en/latest/guide.html
|
||||
.. _Cython: http://cython.org/
|
||||
.. _CFFI: https://cffi.readthedocs.io/en/latest/
|
||||
|
||||
@ -1,134 +0,0 @@
|
||||
#ifndef __CAPSULETHUNK_H
|
||||
#define __CAPSULETHUNK_H
|
||||
|
||||
#if ( (PY_VERSION_HEX < 0x02070000) \
|
||||
|| ((PY_VERSION_HEX >= 0x03000000) \
|
||||
&& (PY_VERSION_HEX < 0x03010000)) )
|
||||
|
||||
#define __PyCapsule_GetField(capsule, field, default_value) \
|
||||
( PyCapsule_CheckExact(capsule) \
|
||||
? (((PyCObject *)capsule)->field) \
|
||||
: (default_value) \
|
||||
) \
|
||||
|
||||
#define __PyCapsule_SetField(capsule, field, value) \
|
||||
( PyCapsule_CheckExact(capsule) \
|
||||
? (((PyCObject *)capsule)->field = value), 1 \
|
||||
: 0 \
|
||||
) \
|
||||
|
||||
|
||||
#define PyCapsule_Type PyCObject_Type
|
||||
|
||||
#define PyCapsule_CheckExact(capsule) (PyCObject_Check(capsule))
|
||||
#define PyCapsule_IsValid(capsule, name) (PyCObject_Check(capsule))
|
||||
|
||||
|
||||
#define PyCapsule_New(pointer, name, destructor) \
|
||||
(PyCObject_FromVoidPtr(pointer, destructor))
|
||||
|
||||
|
||||
#define PyCapsule_GetPointer(capsule, name) \
|
||||
(PyCObject_AsVoidPtr(capsule))
|
||||
|
||||
/* Don't call PyCObject_SetPointer here, it fails if there's a destructor */
|
||||
#define PyCapsule_SetPointer(capsule, pointer) \
|
||||
__PyCapsule_SetField(capsule, cobject, pointer)
|
||||
|
||||
|
||||
#define PyCapsule_GetDestructor(capsule) \
|
||||
__PyCapsule_GetField(capsule, destructor)
|
||||
|
||||
#define PyCapsule_SetDestructor(capsule, dtor) \
|
||||
__PyCapsule_SetField(capsule, destructor, dtor)
|
||||
|
||||
|
||||
/*
|
||||
* Sorry, there's simply no place
|
||||
* to store a Capsule "name" in a CObject.
|
||||
*/
|
||||
#define PyCapsule_GetName(capsule) NULL
|
||||
|
||||
static int
|
||||
PyCapsule_SetName(PyObject *capsule, const char *unused)
|
||||
{
|
||||
unused = unused;
|
||||
PyErr_SetString(PyExc_NotImplementedError,
|
||||
"can't use PyCapsule_SetName with CObjects");
|
||||
return 1;
|
||||
}
|
||||
|
||||
|
||||
|
||||
#define PyCapsule_GetContext(capsule) \
|
||||
__PyCapsule_GetField(capsule, descr)
|
||||
|
||||
#define PyCapsule_SetContext(capsule, context) \
|
||||
__PyCapsule_SetField(capsule, descr, context)
|
||||
|
||||
|
||||
static void *
|
||||
PyCapsule_Import(const char *name, int no_block)
|
||||
{
|
||||
PyObject *object = NULL;
|
||||
void *return_value = NULL;
|
||||
char *trace;
|
||||
size_t name_length = (strlen(name) + 1) * sizeof(char);
|
||||
char *name_dup = (char *)PyMem_MALLOC(name_length);
|
||||
|
||||
if (!name_dup) {
|
||||
return NULL;
|
||||
}
|
||||
|
||||
memcpy(name_dup, name, name_length);
|
||||
|
||||
trace = name_dup;
|
||||
while (trace) {
|
||||
char *dot = strchr(trace, '.');
|
||||
if (dot) {
|
||||
*dot++ = '\0';
|
||||
}
|
||||
|
||||
if (object == NULL) {
|
||||
if (no_block) {
|
||||
object = PyImport_ImportModuleNoBlock(trace);
|
||||
} else {
|
||||
object = PyImport_ImportModule(trace);
|
||||
if (!object) {
|
||||
PyErr_Format(PyExc_ImportError,
|
||||
"PyCapsule_Import could not "
|
||||
"import module \"%s\"", trace);
|
||||
}
|
||||
}
|
||||
} else {
|
||||
PyObject *object2 = PyObject_GetAttrString(object, trace);
|
||||
Py_DECREF(object);
|
||||
object = object2;
|
||||
}
|
||||
if (!object) {
|
||||
goto EXIT;
|
||||
}
|
||||
|
||||
trace = dot;
|
||||
}
|
||||
|
||||
if (PyCObject_Check(object)) {
|
||||
PyCObject *cobject = (PyCObject *)object;
|
||||
return_value = cobject->cobject;
|
||||
} else {
|
||||
PyErr_Format(PyExc_AttributeError,
|
||||
"PyCapsule_Import \"%s\" is not valid",
|
||||
name);
|
||||
}
|
||||
|
||||
EXIT:
|
||||
Py_XDECREF(object);
|
||||
if (name_dup) {
|
||||
PyMem_FREE(name_dup);
|
||||
}
|
||||
return return_value;
|
||||
}
|
||||
|
||||
#endif /* #if PY_VERSION_HEX < 0x02070000 */
|
||||
|
||||
#endif /* __CAPSULETHUNK_H */
|
||||
@ -15,8 +15,6 @@ faq/programming,,::,for x in sequence[::-1]:
|
||||
faq/programming,,:reduce,"print((lambda Ru,Ro,Iu,Io,IM,Sx,Sy:reduce(lambda x,y:x+y,map(lambda y,"
|
||||
faq/programming,,:reduce,"Sx=Sx,Sy=Sy:reduce(lambda x,y:x+y,map(lambda x,xc=Ru,yc=yc,Ru=Ru,Ro=Ro,"
|
||||
faq/windows,,:bd8afb90ebf2,"Python 3.3.0 (v3.3.0:bd8afb90ebf2, Sep 29 2012, 10:55:48) [MSC v.1600 32 bit (Intel)] on win32"
|
||||
howto/cporting,,:encode,"if (!PyArg_ParseTuple(args, ""O:encode_object"", &myobj))"
|
||||
howto/cporting,,:say,"if (!PyArg_ParseTuple(args, ""U:say_hello"", &name))"
|
||||
howto/curses,,:black,"colors when it activates color mode. They are: 0:black, 1:red,"
|
||||
howto/curses,,:red,"colors when it activates color mode. They are: 0:black, 1:red,"
|
||||
howto/curses,,:green,"2:green, 3:yellow, 4:blue, 5:magenta, 6:cyan, and 7:white. The"
|
||||
|
||||
|
Loading…
Reference in New Issue
Block a user