Flask启动后访问出现404 Not Found问题求助（CS50期末项目）

问题描述 #

我正在制作CS50的期末项目，使用云端VS Code环境，执行flask run命令后获得访问URL，但浏览器返回404 Not Found。代码与之前CS50任务的代码非常相似且当时能正常运行，已确认所有HTML文件路径正确，相关代码如下：

from cs50 import SQL
from flask import Flask, flash, redirect, render_template, request, session
from flask_session import Session
from werkzeug.security import check_password_hash, generate_password_hash
import datetime

# Configure application
app = Flask(__name__)

# Ensure templates are auto-reloaded
app.config["TEMPLATES_AUTO_RELOAD"] = True

# Configure session to use filesystem (instead of signed cookies)
app.config["SESSION_PERMANENT"] = False
app.config["SESSION_TYPE"] = "filesystem"
Session(app)

# Configure CS50 Library to use SQLite database
db = SQL("sqlite:///meals.db")


@app.after_request
def after_request(response):
    """Ensure responses aren't cached"""
    response.headers["Cache-Control"] = "no-cache, no-store, must-revalidate"
    response.headers["Expires"] = 0
    response.headers["Pragma"] = "no-cache"
    return response

@app.route("/login", methods=["GET", "POST"])
def login():
    """Log user in"""

    # Forget any user_id
    session.clear()

    # User reached route via POST (as by submitting a form via POST)
    if request.method == "POST":

        # Ensure username was submitted
        if not request.form.get("username"):
            flash("You must provide a username!")
            return render_template("login.html")

        # Ensure password was submitted
        elif not request.form.get("password"):
            flash("You must provide a password!")
            return render_template("login.html")

         # Query database for username
        rows = db.execute("SELECT * FROM users WHERE username = ?", request.form.get("username"))

        # Ensure username exists and password is correct
        if len(rows) != 1 or not check_password_hash(rows[0]["hash"], request.form.get("password")):
            flash("invalid username and/or password")
            return render_template("login.html")

        # Remember which user has logged in
        session["user_id"] = rows[0]["id"]

        # Redirect user to home page
        return redirect("/homepage")

    # User reached route via GET (as by clicking a link or via redirect)
    else:
        return render_template("login.html")

@app.route("/logout")
def logout():
    """Log user out"""

    # Forget any user_id
    session.clear()

    # Redirect user to login form
    return render_template("login.html")

@app.route("/register", methods=["GET", "POST"])
def register():
    """Register user"""
    # If method is POST
    if request.method == "POST":
        name = request.form.get("username")
        password = request.form.get("password")
        confirmation = request.form.get("confirmation")

        # Personal touch - Require users’ passwords to have some number of letters, numbers, and/or symbols
        password_symbols = ['!', '#', '$', '%', '.', '_', '&']

        # Check if any fields are empty
        if not name:
            flash("You must provide a username!")
            return render_template("register.html")
        elif not password:
            flash("You must provide a password!")
            return render_template("register.html")
        elif not confirmation:
            flash("You must confirm tha password!")
            return render_template("register.html")

        # Require users’ passwords to be 8 char long and to have some number of letters, numbers, and/or symbols
        if len(password) < 8:
            flash("Password must be at least 8 characters long!")
            return render_template("register.html")

        if not any(char.isdigit() for char in password):
            flash("Password must have at least one number!")
            return render_template("register.html")

        if not any(char.isupper() for char in password):
            flash("Password must have at least one uppercase!")
            return render_template("register.html")

        if not any(char in password_symbols for char in password):
            flash("must contain at least one symbol of following: ! # $ % . _ &")
            return render_template("register.html")

        # Check if password and confirmation match
        if not password == confirmation:
            flash("Password doesn't match", 400)
            return render_template("register.html")

        # Check if username is taken
        rows = db.execute("SELECT username FROM users WHERE username = ?", name)
        if len(rows) > 0:
            flash("Username is taken", 400)
            return render_template("register.html")

        # Add the new user into the database
        hash = generate_password_hash(password)
        db.execute("INSERT INTO users (username, hash) VALUES(?,?)", name, hash)

        # Remember which user has logged in
        rows = db.execute("SELECT * FROM users WHERE username = ?", request.form.get("username"))
        session["user_id"] = rows[0]["id"]

        # Redirect user to home page
        flash('Registered!')
        return redirect("/homepage")

    # If method is GET
    else:
        return render_template("register.html")

@app.route("/homepage")
def homepage():
    return render_template("homepage.html")

排查与解决方法 #

• 缺少根路由（/）：当前代码未定义@app.route("/")路由，而Flask默认访问的是根路径。直接访问生成的URL时，浏览器请求的是/，但代码中仅配置了/login、/register、/homepage等路由，因此返回404。
  解决：添加根路由，可重定向到登录页或直接渲染页面：

  @app.route("/")
  def index():
      return redirect("/login")  # 或 return render_template("login.html")
  

• 确认访问路径正确性：若未添加根路由，需手动在生成的URL后补充具体路径，例如https://xxx.cs50.io/login或https://xxx.cs50.io/register，而非直接访问根路径。

• 检查Flask入口文件配置：云端VS Code环境中，Flask默认读取app.py作为入口文件。若你的主文件名不是app.py，需先设置环境变量：

  export FLASK_APP=your_filename.py
  

  再执行flask run。

内容的提问来源于stack exchange，提问作者Krisxxx