A Possible Bug in Call Policies

從連結的 pytest_isinstance_issue 重現開始，先分別執行兩個 pytest 檔案，接著執行完整的測試套件。閱讀 callpolicies.cpp、overloading.cpp、test_callpolicies.py 以及對應的 overloading 測試，以比較匯出的 Example 類別和 factory 結果。確定是 Boost.Python、pytest 還是 Python 導致回傳錯誤的類別，並記錄或修正該行為，即視為完成。

Hi, I believe I just encountered a possible bug in boost-python...

First of all, the back story, I'm putting together a python-boost based example for my cmaketools project, which makes a cmake-based python package build as straight-forward as possible. I've taken the examples by TNG (who created his examples based off of the official documentation) and turned them into a package with modules with pytest tests. The modules based on his "09-Overloading" example is failing "08-CallPolicies" example in pytest only when they are run together.

Description

When there is a class with the same name but under different a module (in a same package?), return_value_policy<manage_new_object>() call (possibly?) picks a wrong class to instantiate under pytest running 2 test py files each testing one of the classes.

What is peculiar is that it works when only one test file is tested but fails when both are tested together. So, it could be a pytest issue (or Python's for that matter)...

Versions

Boost: 1.71 (official pre-built binary)
Boost Python DLL: boost_python37-vc142-mt-x64-1_71.dll
Python: 3.7.6 (conda)
Compiler: MSVC 2019 (16.6.1)
OS: Window 10

(Near) Minimal Example

Please find the entire example project at https://github.com/hokiedsp/pytest_isinstance_issue. Clone and run the following to reproduce (hopefully)

pip -e .
pytest tests/test_callpolicies.py # passes
pytest tests/test_nor.py # passes
pytest

Last pytest call fails with the assertion error:

    def test_callpolicies():
        f = policies.Example.factory()
>       assert isinstance(f, policies.Example) and str(f) == "factory"
E       AssertionError: assert (False)
E        +  where False = isinstance(<boost_python_example.overloading.Example object at 0x00000202D58B0300>, <class 'boost_python_example.callpolicies.Example'>)
E        +    where <class 'boost_python_example.callpolicies.Example'> = policies.Example

I'm anticipating f to be boost_python_example.callpolicies.Example but instead boost_python_example.overloading.Example.

Side Note: If CMake cannot find Boost, you need to modify Line 14 of setup.py

configure_opts = ['-DBOOST_ROOT=C:\\Users\\tikum\\AppData\\Local\\Programs\\boost_1_71_0']

code snippets

Here are the sections of most relevant:

callpolicies.cpp

#include <sstream>
#include <string>

class Example {
    Example(std::string n) : mName(n) {}
    std::string mName;
public:
    std::string name() const { return mName; }
    static Example* factory()
    {
        return new Example("factory");
    }
// ... snip...
};

#include <boost/python.hpp>
using namespace boost::python;

BOOST_PYTHON_MODULE(callpolicies)
{
    class_<Example>("Example", no_init)
        .def("__str__", &Example::name)
        .def("factory", &Example::factory,
            return_value_policy<manage_new_object>())
        .staticmethod("factory")
    ;
}	

overloading.cpp

#include <sstream>
#include <string>

class Example {
public:
    Example()
    {}
    // ... snip...
};

#include <boost/python.hpp>
using namespace boost::python;

BOOST_PYTHON_MEMBER_FUNCTION_OVERLOADS(makeIt_overloads, makeIt, 1, 3)
BOOST_PYTHON_MODULE(overloading)
{
    void        (Example::*d1)()             = &Example::doit;
    std::string (Example::*d2)(unsigned int) = &Example::doit;
    void        (Example::*d3)(std::string)  = &Example::doit;

    class_<Example>("Example")
        .def("__str__", &Example::print)
// ...snip...
    ; 
}	

test_callpolicies.py

#!/usr/bin/env python
import pytest
from boost_python_example import callpolicies as policies

def test_callpolicies():
    # e = callpolicies.Example() # won't work, constructore not available from python
    f = policies.Example.factory()
    assert isinstance(f, policies.Example) and str(f) == "factory"