Mailman 3 - Cplusplus-sig

Retiring the Python/C++-sig mailing list
by Jim Bosch June 2, 2025

June 2, 2025

This email list has seen almost no real traffic over the past few years, and I think it's time to retire it. I get the impression that it's largely been supplanted by GitHub issues as a support channel, now that that's where Boost.Python is hosted (in addition to the fact that a lot of people have moved to other libraries for interfacing Python with C++, and those never relied on this list much). Please speak up if you disagree! Jim

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Boost Python help
by Robert Applin May 11, 2024

May 11, 2024

Hi, I'm having problems exposing a C++ class to python using Boost::Python (v1.84). I have defined the following code: class TestClass { public: TestClass() {} }; void test(TestClass& self, std::string const &testStr) { std::cout << "BEFORE" <<std::endl; std::cout << testStr <<std::endl; std::cout << "AFTER" <<std::endl; // ... use self ... } BOOST_PYTHON_MODULE(my_module) { using namespace boost::python; class_<TestClass, std::shared_ptr<TestClass>>("TestClass").def("test", &test); } I then run the following python script: from my_module import TestClass message = "Hello" class_obj = TestClass() class_obj.test(message) but I get the following output: BEFORE Segmentation fault What am I doing wrong? Many thanks in advance, Rob

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Re: [C++-sig] Cplusplus-sig Digest, Vol 139, Issue 1
by daniel marcotte April 13, 2024

April 13, 2024

This would be huge for me! I’ve been adding tags to my user docstrings and generating stub files in python with inspect With the tags, I can emit @overload @staticmethod .etc., but some work is done by hand that leaves room for error On Sun, Apr 14, 2024 at 12:00 AM <cplusplus-sig-request(a)python.org> wrote: > Send Cplusplus-sig mailing list submissions to > cplusplus-sig(a)python.org > > To subscribe or unsubscribe via the World Wide Web, visit > https://mail.python.org/mailman/listinfo/cplusplus-sig > or, via email, send a message with subject or body 'help' to > cplusplus-sig-request(a)python.org > > You can reach the person managing the list at > cplusplus-sig-owner(a)python.org > > When replying, please edit your Subject line so it is more specific > than "Re: Contents of Cplusplus-sig digest..." > > > Today's Topics: > > 1. Emitting complete type information in boost-python docstrings > (Jakob van Santen) > > > ---------------------------------------------------------------------- > > Message: 1 > Date: Fri, 12 Apr 2024 21:48:58 +0200 > From: Jakob van Santen <jvansanten(a)gmail.com> > To: cplusplus-sig(a)python.org > Subject: [C++-sig] Emitting complete type information in boost-python > docstrings > Message-ID: <4D837306-568F-4B41-8523-C497FF0A5204(a)gmail.com> > Content-Type: text/plain; charset="utf-8" > > Hello, > > I?m not sure if this is the right forum for this question (it?s been > pretty quiet here lately), but here goes: > > I have been working on generating PEP 484 type stubs for a large legacy > codebase that is heavily tied to boost-python. This required some > modifications to boost-python itself in order to get complete type > information into the generated docstrings, where it can be consumed by > external tooling to generate stubs: > > https://github.com/boostorg/python/pull/417 > > I have found this quite useful, and suspect it might be useful for others > as well to have it in a Boost release. Can anyone give me a pointer as to > how to make that happen, or let me know where I should be asking instead? > Thanks! > > Cheers, > Jakob > >

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Emitting complete type information in boost-python docstrings
by Jakob van Santen April 12, 2024

April 12, 2024

Hello, I’m not sure if this is the right forum for this question (it’s been pretty quiet here lately), but here goes: I have been working on generating PEP 484 type stubs for a large legacy codebase that is heavily tied to boost-python. This required some modifications to boost-python itself in order to get complete type information into the generated docstrings, where it can be consumed by external tooling to generate stubs: https://github.com/boostorg/python/pull/417 I have found this quite useful, and suspect it might be useful for others as well to have it in a Boost release. Can anyone give me a pointer as to how to make that happen, or let me know where I should be asking instead? Thanks! Cheers, Jakob

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libboost-python: how to create module in C++-runtime and use it from python code, in python 3.x
by Nikolay Shaplov July 23, 2022

July 23, 2022

I have a piece of software that embeds python using libboost-python. It creates a python module in C++ runtime, and then imports it from python code. For python2.7 this works well. See test_module.py and test27.cpp attached. On Debian Stretch it can be build using command g++ test27.cpp -I /usr/include/x86_64-linux-gnu/python2.7 -I /usr/include/ python2.7 -lboost_python -lboost_system -lpython2.7 As I've said It works as expected. Python code imports _hello_provider module that have been created in C++ code, and uses provide_hello() for printing. I've tried to port it to python 3.x, and did not succeed. I managed to write test3x.cpp, it build well on Debian Buster using command g++ test3x.cpp -I /usr/include/x86_64-linux-gnu/python3.9 -I /usr/include/ python3.9 -lpython3.9 -lboost_python39 -lboost_system but it fails when I try to run it. Traceback (most recent call last): File "/usr/lib/python3.9/imp.py", line 169, in load_source module = _exec(spec, sys.modules[name]) File "<frozen importlib._bootstrap>", line 613, in _exec File "<frozen importlib._bootstrap_external>", line 790, in exec_module File "<frozen importlib._bootstrap>", line 228, in _call_with_frames_removed File "test_module.py", line 1, in <module> import _hello_provider ModuleNotFoundError: No module named '_hello_provider' for some reason "native" python module does not see _hello_provider that have been created in runtime. I guess I am doing something wrong, but I am no expert in python and python embedding, and I did not managed to find any good example in the internet. So I guess I need some help here. P.S. If remove "import" related part from examples, it also works well, so the only task here is to make in properly visible... -- Nikolay Shaplov aka Nataraj Fuzzing Engineer at Postgres Professional Matrix IM: @dhyan:nataraj.su

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Multiple Stateless Embedded Python Interpreters with BOOST PYTHON
by AJ D May 18, 2022

May 18, 2022

Hello Python Experts, I had a question on embedding Python interpreter in my application. I have an application where: - I need to embed a Python Interpreter - Run different blocks of Python code on this embedded interpreter - However, each block should not see any of the changes made by the previous block of Python code (except for instances of a particular class which, if created in the first block of Python code, should be visible from the 2nd and subsequent block of Python code) - In other words, for the most part, I would need kind of a fresh Python interpreter for running each block of Python code, with the exception that certain class instances will be shared across all blocks I am using BOOST PYTHON at the moment, since we didn’t want to deal with the lower level details like reference count in Python C API. Wanted some advice on what is the best (production suitable quality-wise) way to get multiple Python interpreters selectively preserve some state and forget all other states? I did some research and came up with the following 4 approaches, wanted to hear some opinion in this forum for/against these approaches: 1. Invoke Py_Initialize() / Py_Finalize() multiple times 1. BOOST Python documentation kind of documents that Py_Finalize() should not be called: https://www.boost.org/doc/libs/1_62_0/libs/python/doc/html/tutorial/tutoria… 2. So, that flow isn’t quite officially supported it looks like. 2. Invoke multiple Python sub-interpreters 1. BOOST Python documentation didn’t seem to talk about sub-interpreters at all – which could mean that it is not supported. 2. I tried it any way and keep getting this error message, which probably is indicating that BOOST Python is trying to re-register the to-Python convertors the 2nd and subsequent time – once again, it didn’t look like a very/officially supported flow. * i. **frozen_importlib:219: RuntimeWarning: to-Python converter for MyClass already registered; second conversion method ignored.* 1. Create the initial Python interpreter in the main process and for executing each Python block fork off a new process and execute each Python block in a child process 1. This would work fine as long as the Python blocks are not writing something back to the data base 2. When Python blocks write something back to the data base, this has to be propagated to the main / parent process i. In multi-threaded environment, this has to be propagated to all active child processes, since eventual consistency isn’t quite allowable in my application domain. 1. Sharing of instances across process can be done using shared memory kind of IPC and serialization using pickle / dill 1. Manually Manage Interpreters 1. Create just 1 interpreter 2. Save its state in some global hash like i. Initial_state = dirs() 1. Use some kind of a lock to allow only 1 block to run at a time (this is acceptable for my application domain) 2. After a block of Python code runs in the interpreter, and before running the next block of Python code, clean up the interpreter using the following approach: i. Walk over globals() and pop everything off / remove from globals() all symbols that is not present (previously saved) in Initial_state – that way any additions by the previous block will not be reachable any more and thus, should be garbage collected. 1. For sharing state across blocks, we may choose to not pop off symbols, based on some condition like instances of a pre-defined class. Any comments / pros / cons on these approaches that I missed? Is there a 5th approach that I missed thinking of? Any pointers is appreciated. Thanks, AD

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Boost Python: Py_TPFLAGS_HAVE_GC flag no traverse function
by Okko Willeboordse April 6, 2022

April 6, 2022

Python 3.11.0a6 (main, Mar 7 2022, 16:46:19) [MSC v.1929 64 bit (AMD64)] on win32 Build Boost Python with Visual Studio 2022. Linking my binding to lib file: boost_python311-vc143-mt-x64-1_78.lib Running my binding with: boost_python311-vc143-mt-x64-1_78.dll Upon loading the binding I get; Traceback (most recent call last): File "<stdin>", line 1, in <module> SystemError: type Boost.Python.enum has the Py_TPFLAGS_HAVE_GC flag but has no traverse function The binding runs without problems with Python 3.8-32 and 3.9-64. Any ideas?

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Problem at linking
by Коростин Андрей Александрович March 15, 2022

March 15, 2022

Hello! I have achieved to a problem and I can't link Boost.Python to my program. I had written my question https://stackoverflow.com/questions/71464470/how-to-link-boost-python-to-a-… but nobody didn't help me. Could you help me or advise who can? Thanks in advance. Sincerely, A. A. Korostin, programmer of the semi-natural modeling sector.

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Boost.Python Installation with all other Boost libaries
by Mayuresh Kedari Jan. 20, 2022

Jan. 20, 2022

Hello, I’m getting errors & didn’t find the correct solution. Error – *C:\boost\boost_1_78_0\boost/python/detail/wrap_python.hpp(57): fatal error C1083: Cannot open include file: 'pyconfig.h': No such file or directory* Why this error is occurring? And also I want to know, how should I escape the whitespace character while specifying the path of Python in the project-config.jam file (On windows..) It would be great if you provide the whole tutorial to install the Boost.Python from scratch along with the other boost libraries on Windows with an msvc toolset. *Thanks & Regards,* *Mayuresh Kedari*

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wrap union types with boost.python
by Malte Dreschert Jan. 16, 2022

Jan. 16, 2022

Hello, I discovered boost.python not long ago and I really like how simple I can wrap my code. I stumbled upon the following struct and don't know how to wrap it. Help is greatly appreciated. struct someStruct { union { float a; float b; }; } Thank you very much, Cheers, Malte

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