使用请求在服务器上发送照片时出现问题

Question

网络摄像机连接到一台单板计算机。使用OpenCV库，我每三分钟接收一次图像，并将其保存在脚本所在的目录中。我希望将照片发送到Web服务器，以便以后查看。要发送图像，我使用了库请求。结果是以下脚本：

import cv2
import time
import serial
import numpy as np
import time
import requests

cap = cv2.VideoCapture(0)
while(1):
    filename1 = time.strftime('Y%m%d-%H%M%S')
    def make_photo():
        cap = cv2.VideoCapture(0)
        for i in range(30):
            cap.read()
            ret, frame = cap.read()


        a = cv2.imwrite(filename1 + '.png', frame)

        cap.release()
        cv2.destroyAllWindows()


        url = 'http://example.com/post.php'

        files = {'file': open(a, 'rb')}

        r = requests.post(url, files = files)
        print(r)

        time.sleep(120)

    def main():
        make_photo()

    if __name__ == '__main__':
        main()

“ post.php”文件包含一个脚本，该脚本接受图像并将其存储在服务器上的目录中。运行python文件时，出现以下错误：

[ WARN:0] terminating async callback
Traceback (most recent call last):
  File "C:/Users/A/PycharmProjects/d/python_mysql_connect2.py", line 39, in <module>
    main()
  File "C:/Users/A/PycharmProjects/d/python_mysql_connect2.py", line 36, in main
    make_photo()
  File "C:/Users/A/PycharmProjects/d/python_mysql_connect2.py", line 28, in make_photo
    r = requests.post(url, files = files)
  File "C:\Users\A\PycharmProjects\d\venv\lib\site-packages\requests\api.py", line 116, in post
    return request('post', url, data=data, json=json, **kwargs)
  File "C:\Users\A\PycharmProjects\d\venv\lib\site-packages\requests\api.py", line 60, in request
    return session.request(method=method, url=url, **kwargs)
  File "C:\Users\A\PycharmProjects\d\venv\lib\site-packages\requests\sessions.py", line 519, in request
    prep = self.prepare_request(req)
  File "C:\Users\A\PycharmProjects\d\venv\lib\site-packages\requests\sessions.py", line 462, in prepare_request
    hooks=merge_hooks(request.hooks, self.hooks),
  File "C:\Users\A\PycharmProjects\d\venv\lib\site-packages\requests\models.py", line 316, in prepare
    self.prepare_body(data, files, json)
  File "C:\Users\A\PycharmProjects\d\venv\lib\site-packages\requests\models.py", line 504, in prepare_body
    (body, content_type) = self._encode_files(files, data)
  File "C:\Users\A\PycharmProjects\d\venv\lib\site-packages\requests\models.py", line 159, in _encode_files
    fdata = fp.read()
OSError: [Errno 9] Bad file descriptor
[ WARN:1] terminating async callback

如何解决此问题？