Flask基础¶
问题143：什么是Flask？如何安装Flask？¶
Flask是一个轻量级的Python Web框架，简单易学，适合快速开发Web应用：
# 安装Flask
# pip install flask
# 基本Flask应用
from flask import Flask
app = Flask(__name__)
@app.route('/')
def hello():
return 'Hello, World!'
if __name__ == '__main__':
app.run(debug=True)
问题144：如何创建Flask应用和路由？¶
from flask import Flask
app = Flask(__name__)
# 基本路由
@app.route('/')
def index():
return '欢迎来到首页'
# 带参数的路由
@app.route('/user/<name>')
def user(name):
return f'你好, {name}!'
# 带类型转换的路由
@app.route('/post/<int:post_id>')
def show_post(post_id):
return f'文章ID: {post_id}'
# 多个路由指向同一个函数
@app.route('/about')
@app.route('/info')
def about():
return '关于我们'
# 指定HTTP方法
@app.route('/login', methods=['GET', 'POST'])
def login():
if request.method == 'POST':
return '登录处理'
return '登录页面'
if __name__ == '__main__':
app.run(debug=True)
问题145：如何处理请求和响应？¶
from flask import Flask, request, jsonify, redirect, url_for
app = Flask(__name__)
# 处理GET请求参数
@app.route('/search')
def search():
query = request.args.get('q', '')
return f'搜索: {query}'
# 处理POST请求数据
@app.route('/submit', methods=['POST'])
def submit():
name = request.form.get('name')
email = request.form.get('email')
return f'提交成功: {name}, {email}'
# 处理JSON数据
@app.route('/api/data', methods=['POST'])
def api_data():
data = request.get_json()
return jsonify({'status': 'success', 'data': data})
# 重定向
@app.route('/redirect')
def redirect_example():
return redirect(url_for('index'))
# 自定义响应
@app.route('/custom')
def custom_response():
from flask import make_response
response = make_response('自定义响应')
response.headers['Content-Type'] = 'text/plain'
return response
if __name__ == '__main__':
app.run(debug=True)
问题146：如何使用Flask模板？¶
from flask import Flask, render_template
app = Flask(__name__)
# 基本模板渲染
@app.route('/')
def index():
return render_template('index.html')
# 传递变量到模板
@app.route('/user/<name>')
def user(name):
return render_template('user.html', name=name)
# 传递多个变量
@app.route('/dashboard')
def dashboard():
user_info = {
'name': '张三',
'age': 25,
'city': '北京'
}
posts = [
{'title': '文章1', 'content': '内容1'},
{'title': '文章2', 'content': '内容2'}
]
return render_template('dashboard.html', user=user_info, posts=posts)
if __name__ == '__main__':
app.run(debug=True)
问题147：如何使用Flask表单处理？¶
from flask import Flask, render_template, request, flash, redirect, url_for
from flask_wtf import FlaskForm
from wtforms import StringField, TextAreaField, SubmitField
from wtforms.validators import DataRequired, Email
app = Flask(__name__)
app.config['SECRET_KEY'] = 'your-secret-key'
# 定义表单类
class ContactForm(FlaskForm):
name = StringField('姓名', validators=[DataRequired()])
email = StringField('邮箱', validators=[DataRequired(), Email()])
message = TextAreaField('消息', validators=[DataRequired()])
submit = SubmitField('提交')
# 处理表单
@app.route('/contact', methods=['GET', 'POST'])
def contact():
form = ContactForm()
if form.validate_on_submit():
flash('消息发送成功！')
return redirect(url_for('contact'))
return render_template('contact.html', form=form)
if __name__ == '__main__':
app.run(debug=True)
问题148：如何使用Flask会话和Cookie？¶
from flask import Flask, session, request, make_response
app = Flask(__name__)
app.config['SECRET_KEY'] = 'your-secret-key'
# 会话管理
@app.route('/login', methods=['POST'])
def login():
username = request.form.get('username')
password = request.form.get('password')
if username == 'admin' and password == 'password':
session['logged_in'] = True
session['username'] = username
return '登录成功'
return '登录失败'
@app.route('/logout')
def logout():
session.pop('logged_in', None)
session.pop('username', None)
return '已退出登录'
@app.route('/profile')
def profile():
if session.get('logged_in'):
return f'欢迎, {session["username"]}!'
return '请先登录'
# Cookie管理
@app.route('/set_cookie')
def set_cookie():
response = make_response('Cookie已设置')
response.set_cookie('user_preference', 'dark_theme')
return response
@app.route('/get_cookie')
def get_cookie():
preference = request.cookies.get('user_preference')
return f'用户偏好: {preference}'
if __name__ == '__main__':
app.run(debug=True)
问题149：如何使用Flask错误处理？¶
from flask import Flask, render_template, abort
app = Flask(__name__)
# 自定义错误页面
@app.errorhandler(404)
def not_found(error):
return render_template('404.html'), 404
@app.errorhandler(500)
def internal_error(error):
return render_template('500.html'), 500
# 手动触发错误
@app.route('/error')
def error():
abort(404)
# 处理特定异常
@app.errorhandler(ValueError)
def handle_value_error(error):
return '值错误', 400
if __name__ == '__main__':
app.run(debug=True)
问题150：如何使用Flask蓝图？¶
from flask import Flask, Blueprint
app = Flask(__name__)
# 创建蓝图
main_bp = Blueprint('main', __name__)
api_bp = Blueprint('api', __name__, url_prefix='/api')
# 在蓝图中定义路由
@main_bp.route('/')
def index():
return '首页'
@main_bp.route('/about')
def about():
return '关于我们'
@api_bp.route('/users')
def get_users():
return {'users': ['张三', '李四', '王五']}
@api_bp.route('/users/<int:user_id>')
def get_user(user_id):
return {'user_id': user_id, 'name': f'用户{user_id}'}
# 注册蓝图
app.register_blueprint(main_bp)
app.register_blueprint(api_bp)
if __name__ == '__main__':
app.run(debug=True)
问题151：如何使用Flask数据库？¶
from flask import Flask, render_template, request, redirect, url_for
from flask_sqlalchemy import SQLAlchemy
app = Flask(__name__)
app.config['SQLALCHEMY_DATABASE_URI'] = 'sqlite:///example.db'
app.config['SQLALCHEMY_TRACK_MODIFICATIONS'] = False
db = SQLAlchemy(app)
# 定义模型
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)
def __repr__(self):
return f'<User {self.username}>'
# 创建表
with app.app_context():
db.create_all()
# 路由
@app.route('/')
def index():
users = User.query.all()
return render_template('index.html', users=users)
@app.route('/add_user', methods=['POST'])
def add_user():
username = request.form['username']
email = request.form['email']
user = User(username=username, email=email)
db.session.add(user)
db.session.commit()
return redirect(url_for('index'))
if __name__ == '__main__':
app.run(debug=True)
问题152：Flask应用的实际部署¶
# 生产环境配置
class Config:
SECRET_KEY = 'your-secret-key'
SQLALCHEMY_DATABASE_URI = 'sqlite:///app.db'
SQLALCHEMY_TRACK_MODIFICATIONS = False
class DevelopmentConfig(Config):
DEBUG = True
class ProductionConfig(Config):
DEBUG = False
# 应用工厂模式
def create_app(config_name='development'):
app = Flask(__name__)
if config_name == 'development':
app.config.from_object(DevelopmentConfig)
else:
app.config.from_object(ProductionConfig)
# 初始化扩展
db.init_app(app)
# 注册蓝图
app.register_blueprint(main_bp)
app.register_blueprint(api_bp)
return app
# 创建应用
app = create_app()
if __name__ == '__main__':
app.run(host='0.0.0.0', port=5000)
总结¶
Flask是一个轻量级的Web框架，主要特点： - 简单易学：核心功能简单，易于理解 - 灵活扩展：通过扩展添加功能 - 模板支持：Jinja2模板引擎 - 路由系统：灵活的路由定义 - 会话管理：内置会话和Cookie支持 - 错误处理：自定义错误页面 - 蓝图系统：模块化应用结构 - 数据库支持：SQLAlchemy集成 - 部署友好：支持多种部署方式