带有硒测试的 Django 频道 2 失败

Question

我正在尝试学习 Django 频道教程。我能够实现here 中描述的聊天功能。但是单元测试从这个page 完全复制粘贴失败，出现以下错误AttributeError: Can't pickle local object 'DaphneProcess.__init__.<locals>.<lambda>'。

完整的追溯：

Traceback (most recent call last):
  File "C:\Users\user\PycharmProjects\django_channels_test\venv35\lib\site-packages\django\test\testcases.py", line 202, in __call__
    self._pre_setup()
  File "C:\Users\user\PycharmProjects\django_channels_test\venv35\lib\site-packages\channels\testing\live.py", line 42, in _pre_setup
    self._server_process.start()
  File "C:\Users\user\AppData\Local\Programs\Python\Python35\Lib\multiprocessing\process.py", line 105, in start
    self._popen = self._Popen(self)
  File "C:\Users\user\AppData\Local\Programs\Python\Python35\Lib\multiprocessing\context.py", line 212, in _Popen
    return _default_context.get_context().Process._Popen(process_obj)
  File "C:\Users\user\AppData\Local\Programs\Python\Python35\Lib\multiprocessing\context.py", line 313, in _Popen
    return Popen(process_obj)
  File "C:\Users\user\AppData\Local\Programs\Python\Python35\Lib\multiprocessing\popen_spawn_win32.py", line 66, in __init__
    reduction.dump(process_obj, to_child)
  File "C:\Users\user\AppData\Local\Programs\Python\Python35\Lib\multiprocessing\reduction.py", line 59, in dump
    ForkingPickler(file, protocol).dump(obj)
AttributeError: Can't pickle local object 'DaphneProcess.__init__.<locals>.<lambda>'

我的消费阶层：

class ChatConsumer(AsyncWebsocketConsumer):
    async def connect(self):
        self.room_name = self.scope['url_route']['kwargs']['room_name']
        self.room_group_name = 'chat_%s' % self.room_name

        # Join room group
        await self.channel_layer.group_add(
            self.room_group_name,
            self.channel_name
        )

        await self.accept()

    async def disconnect(self, close_code):
        # Leave room group
        await self.channel_layer.group_discard(
            self.room_group_name,
            self.channel_name
        )

    # Receive message from WebSocket
    async def receive(self, text_data):
        text_data_json = json.loads(text_data)
        message = text_data_json['message']

        # Send message to room group
        await self.channel_layer.group_send(
            self.room_group_name,
            {
                'type': 'chat_message',
                'message': message
            }
        )

    # Receive message from room group
    async def chat_message(self, event):
        message = event['message']

        # Send message to WebSocket
        await self.send(text_data=json.dumps({
            'message': message
        }))

我的测试模块：

from channels.testing import ChannelsLiveServerTestCase
from selenium import webdriver
from selenium.webdriver.common.action_chains import ActionChains
from selenium.webdriver.support.wait import WebDriverWait


class ChatTests(ChannelsLiveServerTestCase):
    serve_static = True  # emulate StaticLiveServerTestCase

    @classmethod
    def setUpClass(cls):
        super().setUpClass()
        try:
            # NOTE: Requires "chromedriver" binary to be installed in $PATH
            cls.driver = webdriver.Chrome()
        except:
            super().tearDownClass()
            raise

    @classmethod
    def tearDownClass(cls):
        cls.driver.quit()
        super().tearDownClass()

    def test_when_chat_message_posted_then_seen_by_everyone_in_same_room(self):
        try:
            self._enter_chat_room('room_1')

            self._open_new_window()
            self._enter_chat_room('room_1')

            self._switch_to_window(0)
            self._post_message('hello')
            WebDriverWait(self.driver, 2).until(lambda _:
                'hello' in self._chat_log_value,
                'Message was not received by window 1 from window 1')
            self._switch_to_window(1)
            WebDriverWait(self.driver, 2).until(lambda _:
                'hello' in self._chat_log_value,
                'Message was not received by window 2 from window 1')
        finally:
            self._close_all_new_windows()

    def test_when_chat_message_posted_then_not_seen_by_anyone_in_different_room(self):
        try:
            self._enter_chat_room('room_1')

            self._open_new_window()
            self._enter_chat_room('room_2')

            self._switch_to_window(0)
            self._post_message('hello')
            WebDriverWait(self.driver, 2).until(lambda _:
                'hello' in self._chat_log_value,
                'Message was not received by window 1 from window 1')

            self._switch_to_window(1)
            self._post_message('world')
            WebDriverWait(self.driver, 2).until(lambda _:
                'world' in self._chat_log_value,
                'Message was not received by window 2 from window 2')
            self.assertTrue('hello' not in self._chat_log_value,
                'Message was improperly received by window 2 from window 1')
        finally:
            self._close_all_new_windows()

    # === Utility ===

    def _enter_chat_room(self, room_name):
        self.driver.get(self.live_server_url + '/chat/')
        ActionChains(self.driver).send_keys(room_name + '\n').perform()
        WebDriverWait(self.driver, 2).until(lambda _:
            room_name in self.driver.current_url)

    def _open_new_window(self):
        self.driver.execute_script('window.open("about:blank", "_blank");')
        self.driver.switch_to.window(self.driver.window_handles[-1])

    def _close_all_new_windows(self):
        while len(self.driver.window_handles) > 1:
            self.driver.switch_to.window(self.driver.window_handles[-1])
            self.driver.execute_script('window.close();')
        if len(self.driver.window_handles) == 1:
            self.driver.switch_to.window(self.driver.window_handles[0])

    def _switch_to_window(self, window_index):
        self.driver.switch_to.window(self.driver.window_handles[window_index])

    def _post_message(self, message):
        ActionChains(self.driver).send_keys(message + '\n').perform()

    @property
    def _chat_log_value(self):
        return self.driver.find_element_by_css_selector('#chat-log').get_property('value')

我正在使用 Python 3.5 和 Django 2.0。

Answer 1

reduction.py 无法序列化包含 lambda 的对象。经过一番研究，这似乎与 Windows 环境中的多处理问题有关（并且不限于此示例。）

解决此问题的一种方法是reduction.py

替换：import pickle 为 import dill as pickle

dill 包可以序列化这些 pickle 失败的对象。但是，如果不深入研究以确保此更改不会破坏其他任何内容，我不会建议将其用于生产环境。