Python

Table of Contents

• About
• Classes and Functions
• Example Code

About

The Python module allows to execute Python source code. This can be standard Python as well as the classes included in the "c4d" and "maxon" module.

The module's API is defined in the python.framework as well as lib_py.h.

Classes and Functions

• maxon::VirtualMachineInterface represents a language interpreter. The Python 2.7 interpreter can be obtained with MAXON_CPYTHON27VM().
• maxon::VirtualMachineScopeInterface represents a certain code to execute.
• maxon::py::CPythonLibraryInterface represents a library of Python tools.
• maxon::py::CPythonGil represents the global interpreter lock.
• PythonLibrary contains tools to handle classic API elements.

Example Code

// This example function executes the given Python code.
 
#include "maxon/vm.h"
#include "maxon/cpython.h"
#include "maxon/cpython3_raw.h"
#include "maxon/errortypes.h"
#include "c4d_general.h"
#include "c4d_basedocument.h"
#include "lib_py.h"
 
//----------------------------------------------------------------------------------------
// Executes the given Python code.
// @param[in] sourceCode      The source code to execute.
// @param[in] doc             The BaseDocument to set "doc" and "op". If no BaseDocument is set, "doc" and "op" will not be defined.
// @return                    OK on success.
//----------------------------------------------------------------------------------------
static maxon::Result<void> ExecutePythonScript(maxon::String& sourceCode, BaseDocument* doc)
{
  iferr_scope;
 
  // check code
  if (sourceCode.IsEmpty())
    return maxon::IllegalArgumentError(MAXON_SOURCE_LOCATION);
 
  const maxon::VirtualMachineRef&     vm = MAXON_CPYTHON3VM();
  const maxon::VirtualMachineScopeRef scope = vm.CreateScope() iferr_return;
 
  // init script
  iferr (scope.Init("Python Script"_s, sourceCode, maxon::ERRORHANDLING::PRINT, nullptr))
  {
    const String errorMessage = "Error on Init()"_s;
    return maxon::UnknownError(MAXON_SOURCE_LOCATION, errorMessage);
  }
 
  // only set "doc" and "op" if a BaseDocument is set.
  // another option would be to set both "doc" and "op" to None
  if (doc != nullptr)
  {
    // set "doc" and "op" variables
 
    auto python = maxon::Cast<maxon::py::CPythonLibraryRef>(vm.GetLibraryRef());
    maxon::py::CPythonGil gil(python);
 
    // the new Python API from python.framework is compatible with the legacy Python API from lib_py.h.
    // here we temporarily create an old PythonLibrary instance because it can create a PyObject
    // from a BaseDocument and BaseObject
    PythonLibrary pyLib;
 
    auto* pyObjectDoc = pyLib.ReturnGeListNode(doc, false);
    if (pyObjectDoc == nullptr)
      return maxon::UnexpectedError(MAXON_SOURCE_LOCATION);
 
    auto* pyDoc = reinterpret_cast<maxon::py::NativePyObject*>(pyObjectDoc);
    scope.Add("doc"_s, maxon::Data(pyDoc)) iferr_return;
    python.CPy_Decref(pyDoc);
 
 
    BaseObject* op = doc->GetActiveObject();
 
    auto* pyObjectOp = op ? pyLib.ReturnGeListNode(op, false) : pyLib.ReturnPyNone();
    if (pyObjectOp == nullptr)
      return maxon::UnexpectedError(MAXON_SOURCE_LOCATION);
 
    auto* pyOp = reinterpret_cast<maxon::py::NativePyObject*>(pyObjectOp);
    scope.Add("op"_s, maxon::Data(pyOp)) iferr_return;
    python.CPy_Decref(pyOp);
  }
 
  // set __name__ = __main__
  scope.Add("__name__"_s, maxon::Data("__main__"_s)) iferr_return;
 
  // stop all current threads which are potentially modifying the current document,
  // since the active script might modify the currently active document
  StopAllThreads();
 
  // executes the script and returns when it got executed.
  // info: if the script causes an unexpected infinite loop, Execute() does not return
  // and there is no way to stop from the outside.
  iferr (scope.Execute())
  {
    const String errorMessage = "Error on Execute()"_s;
    return maxon::UnknownError(MAXON_SOURCE_LOCATION, errorMessage);
  }
 
  return maxon::OK;
}