Python高级编程：web开发之Flask

1. Flask 简介

Flask 是一个轻量级的 Python Web 应用框架，被称为"微框架"（micro-framework）。它基于 Werkzeug WSGI 工具包和 Jinja2 模板引擎，提供了 Web 开发所需的核心功能，同时保持了高度的灵活性和扩展性。

1.1 Flask 的特点

• 轻量级: 核心简单但是扩展性强

• 灵活性: 不强制特定的项目布局或依赖

• 容易上手: 简单的 API 设计，清晰的文档

• 强大的扩展生态: 丰富的第三方扩展支持

• 活跃的社区: 持续的维护和更新

pip install flask

from flask import Flask

app = Flask(__name__)

@app.route('/')
def hello_world():
    return 'Hello, World!'

if __name__ == '__main__':
    app.run(debug=True)

@app.route('/user')
def user_page():
    return 'User Page'

@app.route('/user/ ') 
def show_user_profile(username):
    return f'User {username}'

@app.route('/post/ ') 
def show_post(post_id):
    return f'Post {post_id}'

@app.route('/login', methods=['GET', 'POST'])
def login():
    if request.method == 'POST':
        return 'Processing login...'
    return 'Please login'

from flask import render_template

@app.route('/hello/ ') 
def hello(name):
    return render_template('hello.html', name=name)

模板文件hello.html:

html>


    Hello Page title>
 head>

    Hello {{ name }}! h1> body> html>

{{ variable }}

{% if user %}
    Hello, {{ user }}!
{% else %}
    Hello, Stranger!
{% endif %}

{% for item in items %}
    

• {{ item }} li> {% endfor %}
• 4. 表单处理4.1 基本表单

from flask import request

@app.route('/submit', methods=['GET', 'POST'])
def submit():
    if request.method == 'POST':
        username = request.form['username']
        password = request.form['password']
        return f'Received: {username}'
    return '''                                                              '''

from flask_wtf import FlaskForm
from wtforms import StringField, PasswordField, SubmitField
from wtforms.validators import DataRequired

class LoginForm(FlaskForm):
    username = StringField('Username', validators=[DataRequired()])
    password = PasswordField('Password', validators=[DataRequired()])
    submit = SubmitField('Login')

from flask_sqlalchemy import SQLAlchemy

app.config['SQLALCHEMY_DATABASE_URI'] = 'sqlite:///test.db'
db = SQLAlchemy(app)

class User(db.Model):
    id = db.Column(db.Integer, primary_key=True)
    username = db.Column(db.String(80), unique=True, nullable=False)
    email = db.Column(db.String(120), unique=True, nullable=False)

from flask_login import LoginManager, UserMixin, login_user, login_required

login_manager = LoginManager()
login_manager.init_app(app)

class User(UserMixin, db.Model):
     # 用户模型定义 
    pass

@login_manager.user_loader
def load_user(user_id):
    return User.query.get(int(user_id))

@app.route('/protected')
@login_required
def protected():
    return 'Protected area'

@app.route('/api/users', methods=['GET'])
def get_users():
    users = User.query.all()
    return jsonify([{'id': user.id, 'username': user.username} for user in users])

@app.route('/api/users/ ', methods=['GET']) 
def get_user(user_id):
    user = User.query.get_or_404(user_id)
    return jsonify({'id': user.id, 'username': user.username})

from flask_restful import Resource, Api

api = Api(app)

class UserResource(Resource):
    def get(self, user_id):
        user = User.query.get_or_404(user_id)
        return {'id': user.id, 'username': user.username}

api.add_resource(UserResource, '/api/users/ ' )

推荐的项目结构：

myproject/
    ├── app/
    │   ├── __init__.py
    │   ├── models.py
    │   ├── routes.py
    │   └── templates/
    ├── config.py
    ├── requirements.txt
    └── run.py

# config.py 
class ProductionConfig:
    DEBUG = False
    SQLALCHEMY_DATABASE_URI = 'postgresql://user:password@localhost/dbname'
    SECRET_KEY = 'your-secret-key'

pip install gunicorn
gunicorn -w 4 -b 127.0.0.1:8000 run:app

@app.errorhandler(404)
def not_found_error(error):
    return render_template('404.html'), 404

@app.errorhandler(500)
def internal_error(error):
    db.session.rollback()
    return render_template('500.html'), 500

import logging
from logging.handlers import RotatingFileHandler

if not app.debug:
    file_handler = RotatingFileHandler('logs/myapp.log', maxBytes=10240, backupCount=10)
    file_handler.setFormatter(logging.Formatter(
        '%(asctime)s %(levelname)s: %(message)s [in %(pathname)s:%(lineno)d]'
    ))
    file_handler.setLevel(logging.INFO)
    app.logger.addHandler(file_handler)

from flask import Blueprint

admin = Blueprint('admin', __name__)

@admin.route('/dashboard')
@login_required
def dashboard():
    return render_template('admin/dashboard.html')

from flask import signals

def handle_user_login(sender, user):
    app.logger.info(f'User {user.username} logged in')

user_logged_in.connect(handle_user_login)

app.run(debug=True)

import unittest

class TestCase(unittest.TestCase):
    def setUp(self):
        self.app = create_app('testing')
        self.client = self.app.test_client()

    def test_home_page(self):
        response = self.client.get('/')
        self.assertEqual(response.status_code, 200)

Flask 是一个强大而灵活的 Web 框架，适合各种规模的项目开发。通过本教程，我们覆盖了从基础到高级的主要开发概念和实践。要成为一个优秀的 Flask 开发者，建议：

1. 深入理解 Flask 的核心概念

2. 熟练掌握常用扩展

3. 遵循最佳实践

4. 注重代码质量和测试

5. 持续学习和实践