I embedded and extended Python 2.7 in my C application a while ago. Late on the train I am bringing it to Python 3, and a lot of initializations for the module registration changed for me.
Before I used PyModule_Create to create the module and added the members afterwards, even sub-modules so I could execute:
from foo.bar import bas
I added/appended the 'top-level' module to PyEval_GetBuiltins(), which might have been wrong in Py 2, but it worked. Now in Py 3 I receive this exception on the code above:
Traceback (most recent call last):
File "foo.py", line 1, in <module>
ModuleNotFoundError: No module named 'foo.bar'; 'foo' is not a package
Looking up the docs, I found now an example with PyImport_ExtendInittab. I have two questions regarding this:
1) What is Inittab supposed to mean? The doc says what it means, but this naming is slighly irritating. What is an Inittab? Shouldn't it be called PyImport_ExtendBuiltins, that I would understand.
2) I can only find examples where plain modules get added. Is creating a package with sub-modules possible with PyImport_ExtendInittab too?
Thanks a lot!
I don't know if what you're trying to pull here (nested extension modules) is OK, anyway the recommended way for structuring code is via [Python 3.Docs]: Modules - Packages.
However, I did this (reproducing the problem, fixing it) as a personal exercise.
Listing the 2 relevant pages:
The environment:
[cfati@CFATI-5510-0:e:\Work\Dev\StackOverflow\q061692747]> tree /a /f Folder PATH listing for volume SSD0-WORK Volume serial number is AE9E-72AC E:. | test00.py | +---py2 | mod.c | \---py3 helper.c mod.c
Dummy module attempting to reproduce the behavior mentioned in the question.
mod.c:
#include <stdio.h>
#include <Python.h>
#define MOD_NAME "mod"
#define SUBMOD_NAME "submod"
static PyObject *pMod = NULL;
static PyObject *pSubMod = NULL;
static PyMethodDef modMethods[] = {
{NULL}
};
PyMODINIT_FUNC initmod() {
if (!pMod) {
pMod = Py_InitModule(MOD_NAME, modMethods);
if (pMod) {
PyModule_AddIntConstant(pMod, "i", -69);
pSubMod = Py_InitModule(MOD_NAME "." SUBMOD_NAME, modMethods);
if (pSubMod) {
PyModule_AddStringConstant(pSubMod, "s", "dummy");
if (PyModule_AddObject(pMod, SUBMOD_NAME, pSubMod) < 0) {
Py_XDECREF(pMod);
Py_XDECREF(pSubMod);
return;
}
}
}
}
}
Output:
[cfati@CFATI-5510-0:e:\Work\Dev\StackOverflow\q061692747\py2]> sopr.bat *** Set shorter prompt to better fit when pasted in StackOverflow (or other) pages *** [prompt]> "f:\Install\pc032\Microsoft\VisualCForPython2\2008\Microsoft\Visual C++ for Python\9.0\vcvarsall.bat" x64 Setting environment for using Microsoft Visual Studio 2008 x64 tools. [prompt]> dir /b mod.c [prompt]> cl /nologo /MD /DDLL /I"c:\Install\pc064\Python\Python\02.07.17\include" mod.c /link /NOLOGO /DLL /OUT:mod.pyd /LIBPATH:"c:\Install\pc064\Python\Python\02.07.17\libs" mod.c Creating library mod.lib and object mod.exp [prompt]> dir /b mod.c mod.exp mod.lib mod.obj mod.pyd mod.pyd.manifest [prompt]> "e:\Work\Dev\VEnvs\py_pc064_02.07.17_test0\Scripts\python.exe" Python 2.7.17 (v2.7.17:c2f86d86e6, Oct 19 2019, 21:01:17) [MSC v.1500 64 bit (AMD64)] on win32 Type "help", "copyright", "credits" or "license" for more information. >>> import sys >>> >>> [item for item in sys.modules if "mod" in item] [] >>> import mod >>> >>> [item for item in sys.modules if "mod" in item] # !!! NOTICE the contents !!! ['mod.submod', 'mod'] >>> >>> mod <module 'mod' from 'mod.pyd'> >>> mod.i -69 >>> mod.submod <module 'mod.submod' (built-in)> >>> mod.submod.s 'dummy' >>> >>> from mod.submod import s >>> s 'dummy' >>>
As seen, importing the module with submodules, adds the submodules in sys.path (didn't look, but I am 99.99% sure this is performed by Py_InitModule)
Conversion to Python 3. Since this is the 1st step, treat the 2 commented lines as they were not there.
mod.c:
#include <stdio.h>
#include <Python.h>
//#include "helper.c"
#define MOD_NAME "mod"
#define SUBMOD_NAME "submod"
static PyObject *pMod = NULL;
static PyObject *pSubMod = NULL;
static PyMethodDef modMethods[] = {
{NULL}
};
static struct PyModuleDef modDef = {
PyModuleDef_HEAD_INIT, MOD_NAME, NULL, -1, modMethods,
};
static struct PyModuleDef subModDef = {
PyModuleDef_HEAD_INIT, MOD_NAME "." SUBMOD_NAME, NULL, -1, modMethods,
};
PyMODINIT_FUNC PyInit_mod() {
if (!pMod) {
pMod = PyModule_Create(&modDef);
if (pMod) {
PyModule_AddIntConstant(pMod, "i", -69);
pSubMod = PyModule_Create(&subModDef);
if (pSubMod) {
PyModule_AddStringConstant(pSubMod, "s", "dummy");
if (PyModule_AddObject(pMod, SUBMOD_NAME, pSubMod) < 0) {
Py_XDECREF(pMod);
Py_XDECREF(pSubMod);
return NULL;
}
//addToSysModules(MOD_NAME "." SUBMOD_NAME, pSubMod);
}
}
}
return pMod;
}
Output:
[cfati@CFATI-5510-0:e:\Work\Dev\StackOverflow\q061692747\py3]> sopr.bat *** Set shorter prompt to better fit when pasted in StackOverflow (or other) pages *** [prompt]> "c:\Install\pc032\Microsoft\VisualStudioCommunity\2017\VC\Auxiliary\Build\vcvarsall.bat" x64 ********************************************************************** ** Visual Studio 2017 Developer Command Prompt v15.9.23 ** Copyright (c) 2017 Microsoft Corporation ********************************************************************** [vcvarsall.bat] Environment initialized for: 'x64' [prompt]> dir /b helper.c mod.c [prompt]> cl /nologo /MD /DDLL /I"c:\Install\pc064\Python\Python\03.07.06\include" mod.c /link /NOLOGO /DLL /OUT:mod.pyd /LIBPATH:"c:\Install\pc064\Python\Python\03.07.06\libs" mod.c Creating library mod.lib and object mod.exp [prompt]> dir /b helper.c mod.c mod.exp mod.lib mod.obj mod.pyd [prompt]> "e:\Work\Dev\VEnvs\py_pc064_03.07.06_test0\Scripts\python.exe" Python 3.7.6 (tags/v3.7.6:43364a7ae0, Dec 19 2019, 00:42:30) [MSC v.1916 64 bit (AMD64)] on win32 Type "help", "copyright", "credits" or "license" for more information. >>> import sys >>> >>> [item for item in sys.modules if "mod" in item] [] >>> import mod >>> >>> [item for item in sys.modules if "mod" in item] # !!! NOTICE the contents !!! ['mod'] >>> >>> mod <module 'mod' from 'e:\\Work\\Dev\\StackOverflow\\q061692747\\py3\\mod.pyd'> >>> mod.i -69 >>> mod.submod <module 'mod.submod'> >>> mod.submod.s 'dummy' >>> >>> from mod.submod import s Traceback (most recent call last): File "<stdin>", line 1, in <module> ModuleNotFoundError: No module named 'mod.submod'; 'mod' is not a package >>> ^Z [prompt]>
As seen, nested import is not possible. That is because mod.submod is not present in sys.modules. As a generalization, "nested" extension submodules are no longer made importable through the module that contains them initialization function. the only option is to import them manually.
As a note: I think this Python 3 restriction is there for a reason, so what comes below is like playing with fire.
Decomment the 2 lines from mod.c.
helper.c:
int addToSysModules(const char *pName, PyObject *pMod) {
PyObject *pSysModules = PySys_GetObject("modules");
if (!PyDict_Check(pSysModules)) {
return -1;
}
PyObject *pKey = PyUnicode_FromString(pName);
if (!pKey) {
return -2;
}
if (PyDict_Contains(pSysModules, pKey)) {
Py_XDECREF(pKey);
return -3;
}
Py_XDECREF(pKey);
if (PyDict_SetItemString(pSysModules, pName, pMod) == -1)
{
return -4;
}
return 0;
}
Output:
[prompt]> cl /nologo /MD /DDLL /I"c:\Install\pc064\Python\Python\03.07.06\include" mod.c /link /NOLOGO /DLL /OUT:mod.pyd /LIBPATH:"c:\Install\pc064\Python\Python\03.07.06\libs" mod.c Creating library mod.lib and object mod.exp [prompt]> "e:\Work\Dev\VEnvs\py_pc064_03.07.06_test0\Scripts\python.exe" Python 3.7.6 (tags/v3.7.6:43364a7ae0, Dec 19 2019, 00:42:30) [MSC v.1916 64 bit (AMD64)] on win32 Type "help", "copyright", "credits" or "license" for more information. >>> >>> import sys >>> >>> [item for item in sys.modules if "mod" in item] [] >>> import mod >>> >>> [item for item in sys.modules if "mod" in item] # !!! NOTICE the contents :) !!! ['mod.submod', 'mod'] >>> >>> from mod.submod import s >>> s 'dummy' >>>
As I stated above, this seems more like a workaraound. A cleaner solution would be to better organize the modules via packages.
Since this is for demo purposes, and to keep the code as simple as possible, I didn't always check Python C API functions return codes. This can lead to hard to find errors (even crashes) and should never be done (especially in production code).
I am not very sure what PyImport_ExtendInittab effect really is as I didn't play with it, but [Python 3.Docs]: Importing Modules - int PyImport_ExtendInittab(struct _inittab *newtab) states (emphasis is mine):
This should be called before Py_Initialize().
So, calling it in our context, is out of the question.
Also mentioning this (old) discussion (not sure whether it contains relevant information, but still) [Python.Mail]: [Python-Dev] nested extension modules?.