old_contents: from PySide import QtGui
  
  from editor import Editor
  
  
  class MainWindow(QtGui.QMainWindow):
      def __init__(self, parent=None):
          super(MainWindow, self).__init__(parent)
          editor = Editor()
          self.setCentralWidget(editor)
          self.setWindowTitle("RST Previewer")
          self.showMaximized()
  
new_contents: from PySide import QtGui, QtCore
  
  from editor import Editor
  
  
  class MainWindow(QtGui.QMainWindow):
      def __init__(self, parent=None):
          super(MainWindow, self).__init__(parent)
          splitter = QtGui.QSplitter(QtCore.Qt.Horizontal)
          treeview =  QtGui.QTreeView()
          editor = Editor()
          self.setCentralWidget(splitter)
  
          splitter.addWidget(treeview)
          splitter.addWidget(editor)
  
          self.setWindowTitle("RST Previewer")
          self.showMaximized()
  
subject: Add splitter with treeview/editor split.