MHO_PyConfigurePath.hh

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#ifndef MHO_PyConfigurePath_HH__
    #define MHO_PyConfigurePath_HH__
 
    #include <sstream>
    #include <string>
 
    #include "MHO_DirectoryInterface.hh"
    #include "MHO_Message.hh"
 
    //pybind11 stuff to interface with python
    #include <pybind11/embed.h>
    #include <pybind11/pybind11.h>
namespace py = pybind11;
 
namespace hops
{
 
static void configure_pypath()
{
    if(Py_IsInitialized() == 0)
    {
        //the internal python interpreter has not been started, bail out
        msg_warn("python_bindings", "python interpreter not running/initialized, cannot configure path " << eom);
    }
    else
    {
        //make sure our python plugin directories are in our search paths
        //only do this once on a per-executable level, since these settings are global
        //(e.g. we don't want each individual class messing with the search paths)
        std::stringstream pyss;
        pyss << "import sys\n";
        //the default plugins dir lives at <install_prefix>/plugin_scripts (resolved at runtime)
        std::string default_path = MHO_DirectoryInterface::GetHopsInstallPrefix();
        if(default_path.empty())
        {
            msg_warn("python_bindings",
                     "could not determine HOPS install prefix; using relative path for default plugins directory" << eom);
            default_path = ".";
        }
        default_path += "/plugin_scripts";
        if(default_path.back() != '/')
        {
            default_path.push_back('/');
        }
        msg_info("main", "adding HOPS_DEFAULT_PLUGINS_DIR to search path: " << default_path << eom);
        pyss << "sys.path.append(\"" << default_path << "\") \n";
 
        //Also add the install tree's python module dir so the embedded interpreter
        //can import the compiled pyMHO_* bindings without the user having to source
        //hops_pypath.sh first.
#ifdef HOPS_PYTHON_SITE_SUBDIR
        {
            std::string site_dir = MHO_DirectoryInterface::GetHopsInstallPrefix();
            if(!site_dir.empty())
            {
                if(site_dir.back() != '/')
                {
                    site_dir.push_back('/');
                }
                site_dir += HOPS_PYTHON_SITE_SUBDIR;
                msg_info("main", "adding HOPS python module dir to search path: " << site_dir << eom);
                pyss << "sys.path.insert(0, \"" << site_dir << "\")\n";
            }
        }
#endif
 
        const char* user_plugin_env = std::getenv("HOPS_USER_PLUGINS_DIR");
        if(user_plugin_env != nullptr)
        {
            std::string user_specified_path = std::string(user_plugin_env);
            if(user_specified_path.back() != '/')
            {
                user_specified_path.push_back('/');
            }
            msg_info("main", "adding HOPS_USER_PLUGINS_DIR to search path: " << user_specified_path << eom);
            pyss << "sys.path.append(\"" << user_specified_path << "\") \n";
        }
 
        //this ensures that python 'print' statements get flushed roughly in sync with when they are called
        //instead of (strangely) at the end of the program
        pyss << "sys.stdout.reconfigure(line_buffering=True)\n";
 
        //now lets make sure pyMHO_Containers and pyMHO_Operators are always present
        pyss << "import pyMHO_Containers\n";
        pyss << "import pyMHO_Operators\n";
        pyss << "import pyMHO_Calibration\n";
 
        //IMPORTANT...if we create additional bindings libraries, we should import them here,
        //otherwise if a user tries to write a plugin but fails to import what they need, they
        //will encounter a cryptic error of the form:
        //terminate called after throwing an instance of 'pybind11::cast_error'
        //  what():  Unable to convert call argument '0' of type '<...something...>' to Python object
        //Aborted (core dumped)
 
        py::exec(pyss.str().c_str());
    }
}
 
} // namespace hops
 
#endif