Python Jython中的用户输入验证

我一直在尝试使用Jython环境为学生进行镜像作业

我正在寻求从用户那里请求一条任意线，我将使用它来镜像图像，这条线必须从图像边缘到边缘，并且是对角线

def userCoordinates():
  pic = makePicture(pickAFile())
  height = getHeight(pic)
  width = getWidth(pic)
  newPic = makeEmptyPicture, (width, height)

startX = requestInteger("Please enter your startX Coordinate")
while startX > width:
  startX = requestInteger("Error, this coordinate is outside the image, please enter your startX Coordinate") 
else:
  print "Your startX coordinate is", startX

startY =  requestInteger("Please enter your startY Coordinate")
while startY > height:
  startY = requestInteger("Error, this coordinate is outside the image, please enter your startY Coordinate")
else:
  print "Your startY coordinate is", startY

endX =  requestInteger("Please enter your endX Coordinate")
while endX > width:
  endX = requestInteger("Error, this coordinate is outside the image, please enter your endX Coordinate")
else:
  print "Your endX coordinate is", endX

endY =  requestInteger("Please enter your endY Coordinate")
while endY > height:
  endY = requestInteger("Error, this coordinate is outside the image, please enter your endY Coordinate")
else:
  print "Your endY coordinate is", endY

是否有任何方法可以验证选定的点是否位于图像的边缘上？或者用一种更好的（更干净的方式）来做上述工作。我在各方面都是初学者

我尝试在startX时使用它！=0或startX！=宽度

但是这样做是行不通的，因为X实际上可以是任何东西

任何帮助都将不胜感激