class addinfourl没有属性＆＃39; __ mro __＆＃39;使用SendGrid时

Question

我正在尝试使用Flask服务器上的SendGrid发送电子邮件。我有一个非常简单的示例代码，如下所示：

    sg = sendgrid.SendGridAPIClient(apikey='key')
    data = {
      "personalizations": [
        {
          "to": [
            {
              "email": "email@gmail.com"
            }
          ],
          "subject": "Hello World from the SendGrid Python Library!"
        }
      ],
      "from": {
        "email": "sender@example.com"
      },
      "content": [
        {
          "type": "text/plain",
          "value": "Hello, Email!"
        }
      ]
    }
    response = sg.client.mail.send.post(request_body=data)
    return jsonify(response)

这导致烧瓶中出现以下错误：

Traceback (most recent call last):
  File "/usr/local/lib/python2.7/site-packages/flask/app.py", line 2000, in __call__
    return self.wsgi_app(environ, start_response)
  File "/usr/local/lib/python2.7/site-packages/flask/app.py", line 1991, in wsgi_app
    response = self.make_response(self.handle_exception(e))
  File "/usr/local/lib/python2.7/site-packages/flask/app.py", line 1567, in handle_exception
    reraise(exc_type, exc_value, tb)
  File "/usr/local/lib/python2.7/site-packages/flask/app.py", line 1988, in wsgi_app
    response = self.full_dispatch_request()
  File "/usr/local/lib/python2.7/site-packages/flask/app.py", line 1641, in full_dispatch_request
    rv = self.handle_user_exception(e)
  File "/usr/local/lib/python2.7/site-packages/flask/app.py", line 1541, in handle_user_exception
    handler = self._find_error_handler(e)
  File "/usr/local/lib/python2.7/site-packages/flask/app.py", line 1476, in _find_error_handler
    .get(code))
  File "/usr/local/lib/python2.7/site-packages/flask/app.py", line 1471, in find_handler
    queue.extend(cls.__mro__)
AttributeError: class addinfourl has no attribute '__mro__'

我无法弄清楚这意味着什么。有人能指出我正确的方向吗？