python - Python:如果JSON响应为空，则无法使用

Question

我只是尝试Platerecognizer.com API来检测矩形框并识别框(牌照)中的每个字符。但API无法读取视频文件，它们只接收jpeg / jpg文件，然后生成JSON。所以我将视频每一帧分开，并发送到API，而我已经完成了。

我有此代码:

from __future__ import absolute_import
from __future__ import division
from __future__ import print_function

import glob
import argparse
import requests
from PIL import Image
import json
import time
import math
import cv2
import os
import json

def main():
    cap = cv2.VideoCapture("assets/car-number-plate.mp4")
    frameRate = cap.get(5)
    print(frameRate)
    seconds=2
    multiplier=frameRate*seconds
    x=1
    while (cap.isOpened()):                                            
            frameId = int(round(cap.get(1)))
            print(frameId)
            ret, frame = cap.read()
            if (ret != True):
                break
            result = []
            if (frameId % multiplier == 0):
                filename = 'output_frame/frameId' +  str(int(x)) + ".jpg"
                cv2.imwrite(filename, frame)
                time.sleep(1)
                path = "/home/mycomputer/Documents/platerecognizer-test/%s" % filename
                with open(path, 'rb') as fp:
                    response = requests.post(
                    'https://api.platerecognizer.com/v1/plate-reader/',
                    files=dict(upload=fp),
                    headers={'Authorization': 'Token ' + 'MY_API_KEY'})
                    result.append(response.json())
                    print(json.dumps(result, indent=2));
                    with open('data.json', 'w') as outfile:
                        json.dump(result, outfile)
                os.remove("%s" %filename)
                x+=1
                time.sleep(1)

                resp_dict = json.loads(json.dumps(result, indent=2))
                num=resp_dict[0]['results'][0]['plate']
                boxs=resp_dict[0]['results'][0]['box']
                xmins,ymins,ymaxs,xmaxs=boxs['xmin'],boxs['ymin'],boxs['ymax'],boxs['xmax']

                cv2.rectangle(frame, (xmins, ymins), (xmaxs, ymaxs), (0, 255, 0), 2)

                font = cv2.FONT_HERSHEY_SIMPLEX
                cv2.putText(frame,num,(xmins, ymins-10), font, 1,(0, 255, 0),2,cv2.LINE_AA)
                cv2.imshow("plat nomor yang terdeteksi",frame)
                cv2.waitKey(0)
                cv2.destroyAllWindows()
                print(f"mobil dengan plat nomor: {num}")
    cap.release()
if __name__ == '__main__':
    main()

上面的代码如何工作？因此，首先我要从目录加载视频，按帧拆分视频，将其发送到API，从API接收完整(非空)响应JSON，如下所示:

[
  {
    "processing_time": 102.465,
    "results": [
      {
        "box": {
          "xmin": 537,
          "ymin": 346,
          "xmax": 657,
          "ymax": 407
        },
        "plate": "b1399ere",
        "region": {
          "score": 0.876,
          "code": "id"
        },
        "vehicle": {
          "score": 0.802,
          "box": {
            "xmin": 163,
            "ymin": 12,
            "xmax": 709,
            "ymax": 472
          },
          "type": "Car"
        },
        "score": 0.898,
        "candidates": [
          {
            "score": 0.898,
            "plate": "b1399ere"
          },
          {
            "score": 0.791,
            "plate": "bi399ere"
          },
          {
            "score": 0.79,
            "plate": "81399ere"
          },
          {
            "score": 0.683,
            "plate": "8i399ere"
          }
        ],
        "dscore": 0.732
      }
    ],
    "filename": "0243_tzJBu_frameId7.jpg",
    "version": 1,
    "camera_id": null,
    "timestamp": "2020-04-20T02:43:34.123444Z"
  }
]

当他们从我们之前发送过图像的json API中找到结果时，代码运行良好，但是当代码找到具有空结果的JSON响应时，则代码如下:

[
  {
    "processing_time": 82.204,
    "results": [],
    "filename": "0243_aKa1u_frameId8.jpg",
    "version": 1,
    "camera_id": null,
    "timestamp": "2020-04-20T02:43:38.881827Z"
  }
]

我只是停留在此错误: IndexError: list index out of range
如果结果JSON为空，我想使此循环工作，然后返回以重新生成上面的下一个捕获帧，并获得具有完整结果的JSON响应。但是，该如何循环？

谢谢

Answer 1

可以将访问结果的代码放入条件中，以仅在结果包含元素时使用结果。

if resp_dict[0]['results']:
        num=resp_dict[0]['results'][0]['plate']
        boxs=resp_dict[0]['results'][0]['box']
                    xmins,ymins,ymaxs,xmaxs=boxs['xmin'],boxs['ymin'],boxs['ymax'],boxs['xmax']
        cv2.rectangle(frame, (xmins, ymins), (xmaxs, ymaxs), (0, 255, 0), 2)
        font = cv2.FONT_HERSHEY_SIMPLEX
        cv2.putText(frame,num,(xmins, ymins-10), font, 1,(0, 255, 0),2,cv2.LINE_AA)
        cv2.imshow("plat nomor yang terdeteksi",frame)
        cv2.waitKey(0)
        cv2.destroyAllWindows()
        print(f"mobil dengan plat nomor: {num}")