我犯了一个低级错误，写下该博客以示警戒：

  我想要现实一张图片，但是搞错了Imshow（）两个参数之间的顺序。导致出现了这个错误

   im = cv2.imread('2007_000032.png')
   cv2.imshow(im,'d')

   cv2.waitKey(0)
   cv2.destroyAllWindows()

/home/dlh/anaconda3/envs/y5/bin/python /home/dlh/opt/dinglinhe/ciwa_segmention/ciwaDataProcess.py
Traceback (most recent call last):
  File "/home/dlh/opt/dinglinhe/ciwa_segmention/ciwaDataProcess.py", line 170, in <module>
    cv2.imshow(im,'d')
SystemError: <built-in function imshow> returned NULL without setting an error

Process finished with exit code 1