python批量转换图片格式：JPEG到jpg

import os
import string
dirName = r"C:\dateset\ImageNet\data\ImageNet2012\ILSVRC2012_bbox_train_v2\Beer\img\\"   #最后要加双斜杠，不然会报错
li=os.listdir(dirName)
for filename in li:
 newname = filename
 newname = newname.split(".")
 if newname[-1]=="JPEG":
  newname[-1]="jpg"
  newname = str.join(".",newname) #这里要用str.join
  filename = dirName+filename
  newname = dirName+newname
  os.rename(filename,newname)
  print(newname,"updated successfully")