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pythonc++python-3.xpython-3.6cpython

embed python environment in c++ application

Using the c-python api I try to embed python 3.6 into a c++ application. However instead of using the system install i'd like to use a virtual environment. I didn't find any documentation on the way to do that. Some related documentation mention 

py_SetProgramName

or 

py_SetPythonHome

Also when reading c-python code i can see the use of pvenv.cfg or ._pth files, but none of these solution seem to work.

Any idea what's the right way to use virtual environment from c api?

EDIT

Let's take a concrete example. I have python installed in

c:\python36

For my c++ application I created a virtual env using the command python -m venv c:\my_cpp_app\python_venv\ in:

c:\my_cpp_app\python_venv\

Using the c-python api I'd like to make my cpp application use the virtual environment located in python_venv instead of c:\python36\

Solution

  • As stated in comments, embedded python 3.6 and virtual environment created with venv seem incompatible (bugs.python.org/issue22213)

    I managed to make it work using virtualenv instead and by calling Py_SetPythonHome prior Py_Initialize. See more details on the python startup sequence

    Locating Python and the standard library

    The location of the Python binary and the standard library is influenced by several elements. The algorithm used to perform the calculation is not documented anywhere other than in the source code. Even that description is incomplete, as it failed to be updated for the virtual environment support added in Python 3.3 (detailed in PEP 405).

    These calculations are affected by the following function calls (made prior to calling Py_Initialize()) and environment variables:

    • Py_SetPythonHome()
    • Py_SetProgramName()
    • PYTHONHOME

    The filesystem is also inspected for pyvenv.cfg files (see PEP 405) or, failing that, a lib/os.py (Windows) or lib/python$VERSION/os.py file.

    The build time settings for PREFIX and EXEC_PREFIX are also relevant, as are some registry settings on Windows. The hardcoded fallbacks are based on the layout of the CPython source tree and build output when working in a source checkout.

    The implementation of pep 587 in later versions should facilitate all this!