Add support for enabling stdout/stderr redirection

This improves the PythonQt module by adding functionality to redirect
stdout and stderr to custom callbacks. It includes methods to enable or
disable redirection and to check if redirection is currently enabled.

(cherry picked from commit commontk/PythonQt@3d3943f)

Author: jcfr

src/PythonQt.cpp

@@ -1871,18 +1871,22 @@ void PythonQt::initPythonQtModule(bool redirectStdOut, const QByteArray& pythonQ
   PythonQtObjectPtr sys;
   sys.setNewRef(PyImport_ImportModule("sys"));
 
-  if (redirectStdOut) {
-    PythonQtObjectPtr out;
-    PythonQtObjectPtr err;
-    // create a redirection object for stdout and stderr
-    out = PythonQtStdOutRedirectType.tp_new(&PythonQtStdOutRedirectType,nullptr, nullptr);
-    ((PythonQtStdOutRedirect*)out.object())->_cb = stdOutRedirectCB;
-    err = PythonQtStdOutRedirectType.tp_new(&PythonQtStdOutRedirectType,nullptr, nullptr);
-    ((PythonQtStdOutRedirect*)err.object())->_cb = stdErrRedirectCB;
-    // replace the built in file objects with our own objects
-    PyModule_AddObject(sys, "stdout", out);
-    PyModule_AddObject(sys, "stderr", err);
-  }
+  // Backup original 'sys.stdout' and 'sys.stderr'
+  PyModule_AddObject(sys, "pythonqt_original_stdout", PyObject_GetAttrString(sys, "stdout"));
+  PyModule_AddObject(sys, "pythonqt_original_stderr", PyObject_GetAttrString(sys, "stderr"));
+
+  // Create a redirection object for stdout and stderr
+  PythonQtObjectPtr out;
+  PythonQtObjectPtr err;
+  out = PythonQtStdOutRedirectType.tp_new(&PythonQtStdOutRedirectType,NULL, NULL);
+  ((PythonQtStdOutRedirect*)out.object())->_cb = stdOutRedirectCB;
+  err = PythonQtStdOutRedirectType.tp_new(&PythonQtStdOutRedirectType,NULL, NULL);
+  ((PythonQtStdOutRedirect*)err.object())->_cb = stdErrRedirectCB;
+  // replace the built in file objects with our own objects
+  PyModule_AddObject(sys, "pythonqt_stdout", out);
+  PyModule_AddObject(sys, "pythonqt_stderr", err);
+
+  setRedirectStdOutCallbackEnabled(redirectStdOut);
 
   // add PythonQt to the list of builtin module names
   PyObject *old_module_names = PyObject_GetAttrString(sys.object(),"builtin_module_names");
@@ -1908,6 +1912,42 @@ void PythonQt::initPythonQtModule(bool redirectStdOut, const QByteArray& pythonQ
 #endif
 }
 
+bool PythonQt::redirectStdOutCallbackEnabled() const
+{
+  PythonQtObjectPtr sys;
+  sys.setNewRef(PyImport_ImportModule("sys"));
+
+  PythonQtObjectPtr pythonqt_stdout;
+  pythonqt_stdout.setNewRef(PyObject_GetAttrString(sys.object(), "pythonqt_stdout"));
+
+  PythonQtObjectPtr stdout;
+  stdout.setNewRef(PyObject_GetAttrString(sys.object(), "stdout"));
+
+  return PyObject_RichCompareBool(pythonqt_stdout.object(), stdout.object(), Py_EQ);
+}
+
+void PythonQt::setRedirectStdOutCallbackEnabled(bool enabled)
+{
+  PythonQtObjectPtr sys;
+  sys.setNewRef(PyImport_ImportModule("sys"));
+
+  if (enabled) {
+    if( PyObject_HasAttrString(sys.object(), "pythonqt_stdout") ) {
+      PyModule_AddObject(sys.object(), "stdout", PyObject_GetAttrString(sys.object(), "pythonqt_stdout"));
+    }
+    if( PyObject_HasAttrString(sys.object(), "pythonqt_stderr") ) {
+      PyModule_AddObject(sys.object(), "stderr", PyObject_GetAttrString(sys.object(), "pythonqt_stderr"));
+    }
+  } else {
+    if( PyObject_HasAttrString(sys.object(), "pythonqt_original_stdout") ) {
+      PyModule_AddObject(sys.object(), "stdout", PyObject_GetAttrString(sys.object(), "pythonqt_original_stdout"));
+    }
+    if( PyObject_HasAttrString(sys.object(), "pythonqt_original_stderr") ) {
+      PyModule_AddObject(sys.object(), "stderr", PyObject_GetAttrString(sys.object(), "pythonqt_original_stderr"));
+    }
+  }
+}
+
 QString PythonQt::getReturnTypeOfWrappedMethod(PyObject* module, const QString& name)
 {
   QStringList tmp = name.split(".");

src/PythonQt.h

@@ -268,6 +268,18 @@ class PYTHONQT_EXPORT PythonQt : public QObject {
 
   //@}
 
+  //---------------------------------------------------------------------------
+  //! \name Standard output handling
+  //@{
+
+  //! return \a true if std out/err redirection is enabled.
+  bool redirectStdOutCallbackEnabled() const;
+
+  //! enable or disable std out/err redirection to pythonStdOut() and pythonStdErr() signals.
+  void setRedirectStdOutCallbackEnabled(bool enabled);
+
+  //@}
+
   //---------------------------------------------------------------------------
   //! \name Modules
   //@{