"Exception in thread" 在 Flask 应用程序中更新键值对时出错
"Exception in thread" error when updating key-value pair in a Flask app
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，我在其中将频道和消息存储为键值对。
消息在一个列表中，所以一对键值看起来像：
{"channelExample" : ["msg1", "msg2"]}。
我还有另一个变量，用于跟踪当前 room/channel 用户正在 currentRoom 中发送消息。
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频道中的消息（emit 已经导入并且我已经确认 currentRoom & 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)& 我不确定为什么。
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
});
下一次，post 完整的回溯以及所有必要的文件，因为这将使调试代码变得更加容易。你说你验证了 currentRoom 是一个字符串值，但可能只是在从浏览器接收到它时。您没有在 submitMessage() 函数中检查它，然后您尝试使用 None 访问您的频道列表，如回溯所示：
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 KeyError，这是因为您将 None 传递给 channels 字典，这意味着 currentRoom 必须是 none.
为什么会这样？问题出在第 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 变量跟在 LEGB rule 之后，这意味着在解析变量名时，解释器将首先检查 L 局部作用域，然后是 Enclosing 作用域，然后是 Global 作用域，最后是 Built-in 作用域。但是，当您 分配 特定范围内的变量时， Python 将在该范围内创建变量。
因此，您现在已经创建了一个名为 currentRoom 的新变量，它是与顶部定义的 currentRoom 分开的 独立 变量，并且仅在 loadMessages() 函数内可见！那么，当您在函数内赋值时，如何让 Python 知道您指的是该全局变量？
您使用了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 submitMessage() 时，currentRoom 现在有一个实际的文本值，而不仅仅是 None，而且函数会成功，没有任何错误。
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，我在其中将频道和消息存储为键值对。
消息在一个列表中，所以一对键值看起来像：
{"channelExample" : ["msg1", "msg2"]}。
我还有另一个变量，用于跟踪当前 room/channel 用户正在 currentRoom 中发送消息。
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频道中的消息（emit 已经导入并且我已经确认 currentRoom & 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)& 我不确定为什么。
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
});
下一次，post 完整的回溯以及所有必要的文件，因为这将使调试代码变得更加容易。你说你验证了 currentRoom 是一个字符串值，但可能只是在从浏览器接收到它时。您没有在 submitMessage() 函数中检查它，然后您尝试使用 None 访问您的频道列表，如回溯所示：
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 KeyError，这是因为您将 None 传递给 channels 字典，这意味着 currentRoom 必须是 none.
为什么会这样？问题出在第 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 变量跟在 LEGB rule 之后，这意味着在解析变量名时，解释器将首先检查 L 局部作用域，然后是 Enclosing 作用域，然后是 Global 作用域，最后是 Built-in 作用域。但是，当您 分配 特定范围内的变量时， Python 将在该范围内创建变量。
因此，您现在已经创建了一个名为 currentRoom 的新变量，它是与顶部定义的 currentRoom 分开的 独立 变量，并且仅在 loadMessages() 函数内可见！那么，当您在函数内赋值时，如何让 Python 知道您指的是该全局变量？
您使用了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 submitMessage() 时，currentRoom 现在有一个实际的文本值，而不仅仅是 None，而且函数会成功，没有任何错误。