想把request中的carcode变为a的第一个值
a = [12,23,45]
request3_header3 = '''UserMsg-length:{\r\n"request_type":"detect",\r\n"request_number":12345,\r\n"production_line_number":1,\r\n"image_type":"JPG",\r\n"image_size":"10240",\r\n"carcode":"xxx",\r\n"car_type":"xxx",\r\n"position":"top",\r\n"time":111,\r\n"image_num":5,\r\n"image_total_num":12\r\n}\r\n'''
UserMsg-length:{
"request_type":"detect",
"request_number":12345,
"production_line_number":1,
"image_type":"JPG",
"image_size":"10240",
"carcode":“xxx”,
"car_type":"xxx",
"position":"top",
"time":111,
"image_num":5,
"image_total_num":12
}
request3_header3['UserMsg-length']['carcode'] = a[0]