Webserver Flask with bootstrap - Take ip address as input to stream with IP Camera

i want some help with my program. My objective is to stream with IP Camera in webserver flask with bootstrap, i figure out how i do that and also i made the web interface like input box and buttons... but the problem is when i wrote the ip address of IP camera in the input box i got this error:

ValueError: View function did not return a response

Looks like it doesn't return the ip address as input from html file to my function in python file.

Here want i have try so far...

html file:

<div class="panel panel-default">
  <div class="panel-heading">
    <h1 class="panel-title">Live Streaming</h1>
  </div>
  <ul class="list-group">
      <li class="list-group-item">Stream with IP Camera:  <span><a href="#" class="btn btn-sm btn-primary" id="IPcambtn">Start</a></span>
      </li>
  </ul>
  <div id="IPcam" class="modal fade" tabindex="-1" role="dialog" aria-labelledby="IPcamlbl" aria-hidden="true">
        <div class="vertical-alignment-helper">
            <div class="modal-dialog modal-sm vertical-align-center">
                <div class="modal-content">
                    <div class="modal-header">
                        <button type="button" class="close" data-dismiss="modal" aria-hidden="true">&times;</button>
                        <h4 class="modal-title" id="IPcambl">Enter camera's IP address:</h4>
                    </div>
                    <div class="modal-body">
                        <form action="" role="form" id="IPcam" method="post">
                            <input type="hidden" name="formType" value="IPcam">
                            <div class="form-group">
                            <label for="basic-url">IP Address:</label>
                            <div class="input-group mb-3">
                              <div class="input-group-prepend">
                                <span class="input-group-text" id="basic-addon3">rtsp://</span>
                              </div>
                              <input name="IPaddress" type="text" class="form-control" id="basic-url" aria-describedby="basic-addon3" style="width: 275px;>
                            </div>
                                </div>
                            </div>
                            <div class="form-group">
                                <div class="col-xs- col-xs-offset- text-center">
                                    <!-- Do NOT use name="submit" or id="submit" for the Submit button -->

                                    <button type="submit" class="btn btn-danger" tabindex="3">Confirm</button>
                                <div class="panel-body">
                                  <img id="pic" src="" class="img-responsive img-rounded"></img>
                              </div>
                          </div>
                      </form>
                  </div>
              </div>
          </div>
      </div>
  </div>

python file:

class Stream(flask.views.MethodView):
    @login_required
    def get(self):
        return flask.render_template('stream.html')
    def post(self):
        formType = flask.request.form.get('formType')
        IPcamPass = ""
        if formType == "IPcam":
            required = ['IPaddress']
            for r in required:
                    IPcamPass += flask.request.form.get(r)
            print ("Connecting with IP Camera...")
            database().writeLogs("IP Camera connection established")
            flask.flash("You are now connected with IP Camera")
            IPstream()

#Functions for IP Camera streaming.
@app.route('/IPstream')
def IPstream():
    return Response(IPcam(),mimetype='multipart/x-mixed-replace; boundary=frame')
    return ""
def IPcam():  
    camera = cv2.VideoCapture(IPaddress)
    while True:
        success, frame = camera.read()  # read the camera frame
        if not success:
             break
        else:
             ret, buffer = cv2.imencode('.jpg', frame)
             frame = buffer.tobytes()
             yield (b'--frame\r\n'b'Content-Type: image/jpeg\r\n\r\n' + frame + b'\r\n')  # concat frame one by one and show result

Error:

Traceback (most recent call last)

    File "/usr/lib/python2.7/dist-packages/flask/app.py", line 1997, in __call__

    return self.wsgi_app(environ, start_response)

    File "/usr/local/lib/python2.7/dist-packages/werkzeug/middleware/proxy_fix.py", line 228, in __call__

    return self.app(environ, start_response)

    File "/usr/lib/python2.7/dist-packages/flask/app.py", line 1985, in wsgi_app

    response = self.handle_exception(e)

    File "/usr/lib/python2.7/dist-packages/flask/app.py", line 1540, in handle_exception

    reraise(exc_type, exc_value, tb)

    File "/usr/lib/python2.7/dist-packages/flask/app.py", line 1982, in wsgi_app

    response = self.full_dispatch_request()

    File "/usr/lib/python2.7/dist-packages/flask/app.py", line 1615, in full_dispatch_request

    return self.finalize_request(rv)

    File "/usr/lib/python2.7/dist-packages/flask/app.py", line 1630, in finalize_request

    response = self.make_response(rv)

    File "/usr/lib/python2.7/dist-packages/flask/app.py", line 1725, in make_response

    raise ValueError('View function did not return a response')

    ValueError: View function did not return a response