Python PyQt:self.setScene（self.scene）属性错误：'；窗口'；对象没有属性'；setScene'；

目的是查看窗口中的滚动条：
绘制滚动条的功能取自此处：

这个错误意味着什么？我应该怎么解决它

import sys

from PyQt4 import QtGui
from PyQt4 import QtCore

from PyQt4.QtGui import QMainWindow, QSizePolicy, QWidget, QVBoxLayout, QAction,\
        QKeySequence, QLabel, QItemSelectionModel, QMessageBox, QFileDialog, QFrame, \
        QDockWidget, QProgressBar, QProgressDialog

from PyQt4.QtCore import SIGNAL, QSettings, QSize, QPoint, QVariant, QFileInfo, QTimer, pyqtSignal, QObject


class Window(QtGui.QMainWindow):

  def __init__(self, parent=None):

        QtGui.QGraphicsView.__init__(self, parent)
        self.scene = QtGui.QGraphicsScene(self)
        self.scene.setBackgroundBrush(QtGui.QBrush(QtCore.Qt.darkGray, QtCore.Qt.SolidPattern))
        self.setScene(self.scene)

        self.setDragMode(QtGui.QGraphicsView.ScrollHandDrag)
        self.setTransformationAnchor(QtGui.QGraphicsView.AnchorUnderMouse)
        self.viewport().setCursor(QtCore.Qt.CrossCursor)
        self.setHorizontalScrollBarPolicy(QtCore.Qt.ScrollBarAlwaysOff)
        self.setVerticalScrollBarPolicy(QtCore.Qt.ScrollBarAlwaysOff)

        self._pan = False
        self._draw = False
        self._moved = False
        self._sel = False
        self.pen = None
        self.penid = None
        self.cmap = None
        self.penwidth = 4
        self._redoStack = []
        self._histStates = []
        self._baseRects = [] 

app = QtGui.QApplication(sys.argv)
GUI = Window()
sys.exit(app.exec_())

错误：

Traceback (most recent call last):
  File "temp.py", line 42, in <module>
    GUI = Window()
  File "temp.py", line 21, in __init__
    self.setScene(self.scene)
AttributeError: 'Window' object has no attribute 'setScene'

回溯（最近一次呼叫最后一次）：
文件“temp.py”，第42行，在
GUI=Window（）
文件“temp.py”，第21行，在_init中__
self.setScene（self.scene）
AttributeError:“Window”对象没有属性“setScene”

您表示

窗口是
QMainWindow
：

class Window(QtGui.QMainWindow):

因此，
窗口
不是QGraphicsView

因此，在显示此隐式窗口必须是
QGraphicsView
的示例中，解决方案是将
QMainWindow
更改为
QGraphicsView

import sys

from PyQt4 import QtGui
from PyQt4 import QtCore

class Window(QtGui.QGraphicsView):

  def __init__(self, parent=None):

        QtGui.QGraphicsView.__init__(self, parent)
        self.scene = QtGui.QGraphicsScene(self)
        self.scene.setBackgroundBrush(QtGui.QBrush(QtCore.Qt.darkGray, QtCore.Qt.SolidPattern))
        self.setScene(self.scene)

        self.setDragMode(QtGui.QGraphicsView.ScrollHandDrag)
        self.setTransformationAnchor(QtGui.QGraphicsView.AnchorUnderMouse)
        self.viewport().setCursor(QtCore.Qt.CrossCursor)
        self.setHorizontalScrollBarPolicy(QtCore.Qt.ScrollBarAlwaysOff)
        self.setVerticalScrollBarPolicy(QtCore.Qt.ScrollBarAlwaysOff)

        self._pan = False
        self._draw = False
        self._moved = False
        self._sel = False
        self.pen = None
        self.penid = None
        self.cmap = None
        self.penwidth = 4
        self._redoStack = []
        self._histStates = []
        self._baseRects = [] 

app = QtGui.QApplication(sys.argv)
GUI = Window()
GUI.show()
sys.exit(app.exec_())