I'm using pythonnet to embed python 3.6 in a C# WPF application. I'm effectively booting up a venv with pythonnet and I noticed the user site folder kept getting included in sys.path.

There is a command line argument to disable this, (-S, more info here: https://docs.python.org/3/using/cmdline.html#id3) but as pythonnet loads python directly, this won't work.

There is a way to access this flag with the C API, info here: https://docs.python.org/3/c-api/init.html#c.Py_NoSiteFlag

This is a global variable that is exported, defined here: https://github.com/python/cpython/blob/3.6/Include/pydebug.h

My particular use case is for python 3.6, but it appears this flag is present in 2.7 and all currently supported 3.x versions.

Here is an example on how I am using this addition:

PythonEngine.PythonHome = pythonHome;
PythonEngine.PythonPath = pythonPath;
PythonEngine.SetNoSiteFlag();
PythonEngine.Initialize();

It seems to do the business and I no longer get the user site package path in sys.path.

Note: I'm not quite sure how to test this addition as really is dependent on the user's environment. Perhaps a test to verify the global var is set to 1? Please let me know your thoughts.