只需按照相同的示例添加第三个命令：
p1 = subprocess.Popen(['convert', fileIn, 'bmp:-'], stdout=subprocess.PIPE)p2 = subprocess.Popen(['mkbitmap', '-f', '2', '-s', '2', '-t', '0.48'], stdin=p1.stdout, stdout=subprocess.PIPE)p1.stdout.close()p3 = subprocess.Popen(['potrace', '-t' , '5', '-s' , '-o', fileOut], stdin=p2.stdout,stdout=subprocess.PIPE)p2.stdout.close()output = p3.communicate()[0]
