Runs python from nix as a function (Run with: --option allow-unsafe-native-code-during-evaluation true)

pythonEval.nix

{ runCommand, python, nix, boehmgc }:

let
  eval-python-src = builtins.toFile "eval-python.cc" ''
    #include <Python.h>
    #include <eval.hh>
    #include <gc/gc.h>
    #include <gc/gc_cpp.h>

    #define NEW new (UseGC)

    using namespace std;
    using namespace nix;

    void prim_evalPython(EvalState& state, const Pos& pos, Value** args, Value& v) {
      string catch_output =
    "import sys\n\
    class CatchOut:\n\
        def __init__(self):\n\
            self.value = \"\"\n\
        def write(self, txt):\n\
            self.value += txt\n\
    catchOutErr = CatchOut()\n\
    catchOut = CatchOut()\n\
    sys.stdout = catchOut\n\
    sys.stderr = catchOutErr\n\
    "; //this is python code to redirect stdouts/stderr

      PathSet context;
      string code = state.coerceToString(pos, *args[0], context);

      Py_Initialize();
      PyObject *pModule = PyImport_AddModule("__main__");
      PyRun_SimpleString(catch_output.c_str());
      PyRun_SimpleString(code.c_str());
      PyErr_Print();

      PyObject *catcher = PyObject_GetAttrString(pModule, "catchOutErr");
      PyObject *error = PyObject_GetAttrString(catcher, "value");
      std::string error_s(PyString_AsString(error));
      if (error_s.size()>0) throw EvalError(error_s);

      catcher = PyObject_GetAttrString(pModule, "catchOut");
      PyObject *output = PyObject_GetAttrString(catcher, "value");
      string output_s(PyString_AsString(output));

      mkString(v, output_s, PathSet());
      Py_Finalize();
    }

    extern "C" void initialize(EvalState& state, Value& v) {
      v.type = tPrimOp;
      v.primOp = NEW PrimOp(prim_evalPython, 1, state.symbols.create("evalPython"));
    }
  '';

  eval-python-so = runCommand "eval-python.so" {} ''
    c++ -shared -fPIC -L${python}/lib/ -lpython2.7 -I${nix}/include/nix -I${boehmgc}/include -I${python}/include/python2.7/ -std=c++11 -O3 ${eval-python-src} -o $out
    strip $out
  '';

in builtins.importNative eval-python-so "initialize"