javascript - 在 Flask 应用程序中更新键值对时出现“线程异常”错误
问题描述
我正在构建一个基本的聊天程序(来自 CS50s 网络编程的 Flack)。
我有一本字典,我将频道和消息存储为键值对。
消息在一个列表中,所以一个键值对看起来像:
{"channelExample" : ["msg1", "msg2"]}
.
我还有另一个变量来跟踪用户正在发送消息的当前房间/频道,称为currentRoom。
当用户提交消息时,我正在尝试通过执行以下操作来更新该通道中的消息(已经导入了emit并且我已经确认currentRoom和输入消息是字符串值):
@socketio.on("submit message")
def submitMessage(message):
channels[currentRoom].append(message)
emit("display message", message)
但是我被抛出一个“线程中的异常...... ”错误,channels[currentRoom].append(message)
我不知道为什么。
我在 Flask 中的完整代码:
import os
from flask import Flask, session, render_template, url_for, request, flash, redirect, jsonify
from flask_socketio import SocketIO, send, emit, join_room, leave_room
app = Flask(__name__)
app.config["SECRET_KEY"] = os.getenv("SECRET_KEY")
socketio = SocketIO(app)
currentRoom = None
channels = {}
@app.route("/")
def index():
return render_template("welcome.html", channels=channels)
@socketio.on("new channel")
def newChannel(channelName):
# Store new channel to keep track of it
channels.update( {channelName : []} )
@socketio.on("retrieve channels")
def retrieveChannels():
channelNames = []
for channel in channels:
channelNames.append(channel)
emit("providing channels", channelNames)
@socketio.on("retrieve messages")
def loadMessages(channelName):
currentRoom = channelName
channelMessages = channels[currentRoom]
emit("load messages", channelMessages)
@socketio.on("submit message")
def submitMessage(message):
channels[currentRoom].append(message)
emit("display message", message)
Javascript:
document.addEventListener('DOMContentLoaded', () => {
// Connect to websocket
var socket = io.connect(location.protocol + '//' + document.domain + ':' + location.port);
// When connected,
socket.on('connect', () => {
var nameInput = document.querySelector("#usernameInput");
var welcomeMessage = document.querySelector("#welcomeMessage");
var createChannel = document.querySelector("#createChannel");
var newChannelForm = document.querySelector("#newChannelForm");
var newMessageForm = document.querySelector("#newMessageForm");
function userExists() {
// Check if user has come here before
if (localStorage.getItem("username")) {
// Display a welcome message
welcomeMessage.innerHTML = `Welcome back ${localStorage.getItem("username")}!`;
nameInput.style.display = "none";
return true;
}
else {
return false;
}
};
function createChannelBtn(name) {
// Create new channel & style it
let newChannel = document.createElement("button");
newChannel.id = name;
newChannel.innerHTML = name;
newChannel.className = "btn btn-block btn-outline-dark";
newChannel.style.display = "block";
// Attach to current list
document.querySelector("#channels").appendChild(newChannel);
// When someone clicks the channel
newChannel.onclick = () => {
newChannel.classList.toggle("active");
socket.emit("retrieve messages", newChannel.id);
console.log("Retrieving messages!!!");
socket.on("load messages", channelMessages => {
console.log("loading messages!");
for (let i = 0; i < channelMessages.length; i++) {
createMessage(channelMessages[i]);
}
});
};
};
function createMessage(messageContent) {
let message = document.createElement("h6");
message.innerHTML = messageContent;
document.querySelector("#messageWindow").appendChild(message);
console.log("Currently creating message!");
};
function loadChannels() {
socket.emit("retrieve channels")
socket.on("providing channels", channelNames => {
for (let i = 0; i < channelNames.length; i++) {
createChannelBtn(channelNames[i]);
}
});
};
// Make sure the new channel form is not displayed until "Create channel" button is clicked
newChannelForm.style.display = "none";
// Check if user exists already in local storage
userExists();
loadChannels();
// If someone submits a username...
nameInput.addEventListener("click", () => {
// if that username exists, do nothing
if (userExists()) {
}
// else remember the username
else {
localStorage.setItem("username", document.querySelector("#user").value);
}
});
// When someone wants to create a channel
createChannel.addEventListener("click", () => {
// Show form
newChannelForm.style.display = "block";
// When user inputs new channel name...
newChannelForm.onsubmit = () => {
// Retrieve their input
var newChannelName = document.querySelector("#newChannel").value;
// Create a new channel
createChannelBtn(newChannelName);
// Notify server to store new channel
socket.emit("new channel", newChannelName);
// Clear input field
document.querySelector("#newChannel").innerHTML = "";
return false;
};
});
newMessageForm.onsubmit = () => {
let message = document.querySelector("#newMessage").value;
console.log("You have entered " + message);
socket.emit("submit message", message);
console.log("Submitted message!");
socket.on("display message", message => {
createMessage(message);
console.log("Displaying message!!");
});
return false;
};
});
// DOM Ending Bracket
});
解决方案
下一次,发布完整的回溯,以及所有必要的文件,因为这将使您的代码更容易调试。您说您验证了这currentRoom
是一个字符串值,但可能仅在从浏览器接收到它时。您没有在您的submitMessage()
函数中检查它,然后您尝试使用 访问您的频道列表None
,如回溯所示,看起来像这样:
Exception in thread Thread-13:
Traceback (most recent call last):
File "C:\Users\Michael\AppData\Local\Programs\Python\Python37-32\lib\threading.py", line 917, in _bootstrap_inner
self.run()
File "C:\Users\Michael\AppData\Local\Programs\Python\Python37-32\lib\threading.py", line 865, in run
self._target(*self._args, **self._kwargs)
File "c:\Users\Michael\Desktop\sandbox\sandbox\lib\site-packages\socketio\server.py", line 640, in _handle_event_internal
r = server._trigger_event(data[0], namespace, sid, *data[1:])
File "c:\Users\Michael\Desktop\sandbox\sandbox\lib\site-packages\socketio\server.py", line 669, in _trigger_event
return self.handlers[namespace][event](*args)
File "c:\Users\Michael\Desktop\sandbox\sandbox\lib\site-packages\flask_socketio\__init__.py", line 280, in _handler
*args)
File "c:\Users\Michael\Desktop\sandbox\sandbox\lib\site-packages\flask_socketio\__init__.py", line 694, in _handle_event
ret = handler(*args)
File "c:\Users\Michael\Desktop\sandbox\sandbox.py", line 47, in submitMessage
channels[currentRoom].append(message)
KeyError: None
这应该提醒您,您主要关心的是 a KeyError
,这是因为您正在传递None
给您的channels
dict ,这意味着它currentRoom
一定不是。
那么为什么会这样呢?问题在于第 34 行:
32 @socketio.on("retrieve messages")
33 def loadMessages(channelName):
34 currentRoom = channelName # <--- Issue here
35
36 channelMessages = channels[currentRoom]
37
38 emit("load messages", channelMessages)
Python 变量遵循LEGB 规则,这意味着在解析变量名时,解释器将首先检查L本地范围,然后是E封闭范围,然后是全局范围,最后是内置范围。但是,当您在某个范围内分配变量时,Python 将在该范围内创建该变量。
因此,您现在已经创建了一个名为 的新变量currentRoom
,它是一个独立于顶部定义的变量currentRoom
,并且仅在loadMessages()
函数中可见!那么,当你在一个函数中赋值时,你如何让 Python 知道你指的是那个全局变量呢?
您使用global
关键字:
@socketio.on("retrieve messages")
def loadMessages(channelName):
global currentRoom # <--- This tells Python that `currentRoom` is a global variable
currentRoom = channelName # Assign to the global variable
channelMessages = channels[currentRoom]
emit("load messages", channelMessages)
现在,当我们调用 时submitMessage()
,currentRoom
现在有一个实际的文本值,而不仅仅是None
,并且函数成功且没有任何错误。
推荐阅读
- python-3.x - 有没有办法连接字符串中的字符,以便字母之间没有空格?
- python - 运行 Python 时隐藏终端
- string - 如何在另一个中调用这个函数?
- ios - 如何让我的 JSON 数据显示在 tableview 中
- amazon-web-services - ECS 实例无法排空?
- java - 从无限匹配列表输入制作足球排名
- python - Pandas - 过滤另一列中只有一个值的列的值
- amazon-quicksight - Quicksight - 比较本周(未完成)的销售额与上周(苹果对苹果)的销售额
- python - 将项目添加到库存
- python - pyhoton dict和list,我做了大部分工作需要一些帮助