Flask文档

1. 快速入门(Quickstart)

1.1 最小的Flask应用

from flask import Flask
app = Flask(__name__)

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

1.2 路由(Routing)

应用route()装饰器建立函数对地址(URL)的映射。

@app.route('/')
def index():
    return 'Index Page'

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

1.3 变量规则(Variable Rules)

You can add variable sections to a URL by marking sections with <variable_name>. Your function then receives the <variable_name> as a keyword argument.

Optionally, you can use a converter to specify the type of the argument like <converter:variable_name>.

@app.route('/user/<username>')
def show_user_profile(username):
    # show the user profile for that user
    return 'User %s' % username

@app.route('/post/<int:post_id>')
def show_post(post_id):
    # show the post with the given id, the id is an integer
    return 'Post %d' % post_id

@app.route('/path/<path:subpath>')
def show_subpath(subpath):
    # show the subpath after /path/
    return 'Subpath %s' % subpath

1.4 唯一URLs/重定向行为(Unique URLs / Redirection Behavior)

@app.route('/projects/')
def projects():
    return 'The project page'

@app.route('/about')
def about():
    return 'The about page'

The canonical URL for the projects endpoint has a trailing slash. It’s similar to a folder in a file system. If you access the URL without a trailing slash, Flask redirects you to the canonical URL with the trailing slash.

The canonical URL for the about endpoint does not have a trailing slash. It’s similar to the pathname of a file. Accessing the URL with a trailing slash produces a 404 “Not Found” error. This helps keep URLs unique for these resources, which helps search engines avoid indexing the same page twice.

1.5 构建URL(URL Building)

To build a URL to a specific function, use the url_for() function. It accepts the name of the function as its first argument and any number of keyword arguments.

from flask import Flask, url_for

app = Flask(__name__)

@app.route('/')
def index():
    return 'index'

@app.route('/login')
def login():
    return 'login'

@app.route('/user/<username>')
def profile(username):
    return '{}\'s profile'.format(username)

with app.test_request_context():
    print(url_for('index'))
    print(url_for('login'))
    print(url_for('login', next='/'))
    print(url_for('profile', username='John Doe'))

1.6 HTTP方法

from flask import request

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

1.7 静态文件(Static Files)

Just create a folder called static in your package or next to your module and it will be available at /static on the application.

To generate URLs for static files, use the special 'static' endpoint name:

url_for('static', filename='style.css')

The file has to be stored on the filesystem as static/style.css.

1.8 渲染模板

Flask应用Jinja2来自动创建模板。

To render a template you can use the render_template() method.

from flask import render_template

@app.route('/hello/')
@app.route('/hello/<name>')
def hello(name=None):
    return render_template('hello.html', name=name)

Flask will look for templates in the templates folder. So if your application is a module, this folder is next to that module, if it’s a package it’s actually inside your package:

# Case 1: a module
/application.py
/templates
    /hello.html

# Case 2: a package
/application
    /__init__.py
    /templates
        /hello.html

Here is an example template

<!doctype html>
<title>Hello from Flask</title>
{% if name %}
  <h1>Hello {{ name }}!</h1>
{% else %}
  <h1>Hello, World!</h1>
{% endif %}

1.9 请求对象

当前请求的方法可以用 method 属性来访问。你可以用 form 属性来访问表单数据 (数据在 POST 或者 PUT 中传输)。

@app.route('/login', methods=['POST', 'GET'])
def login():
    error = None
    if request.method == 'POST':
        if valid_login(request.form['username'],
                       request.form['password']):
            return log_the_user_in(request.form['username'])
        else:
            error = 'Invalid username/password'
    # the code below this is executed if the request method
    # was GET or the credentials were invalid
    return render_template('login.html', error=error)

你可以用 args 属性来接收在 URL ( ?key=value ) 中提交的参数

searchword = request.args.get('key', '')

1.10 Cookies

请求对象中的 cookies 属性是一个客户端发送所有的 cookies 的字典。

读取 cookies

from flask import request

@app.route('/')
def index():
    username = request.cookies.get('username')
    # use cookies.get(key) instead of cookies[key] to not get a
    # KeyError if the cookie is missing.

存储 cookies

from flask import make_response

@app.route('/')
def index():
    resp = make_response(render_template(...))
    resp.set_cookie('username', 'the username')
    return resp

1.11 重定向和错误

你能够用 redirect() 函数重定向用户到其它地方。能够用 abort() 函数提前中断一个请求并带有一个错误代码。这里是一个它们如何工作的例子：

from flask import abort, redirect, url_for

@app.route('/')
def index():
    return redirect(url_for('login'))

@app.route('/login')
def login():
    abort(401)
    this_is_never_executed()

默认情况下，每个错误代码会显示一个黑白错误页面。如果你想定制错误页面，可以使用 errorhandler() 装饰器

from flask import render_template

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

1.12 关于响应

如果你想要获取在视图中得到的响应对象，你可以用函数 make_response() 。

想象你有这样一个视图

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

你只需要用 make_response() 封装返回表达式，获取结果对象并修改，然后返回它

@app.errorhandler(404)
def not_found(error):
    resp = make_response(render_template('error.html'), 404)
    resp.headers['X-Something'] = 'A value'
    return resp

1.13 会话

除了请求对象，还有第二个称为 session 对象允许你在不同请求间存储特定用户的信息。这是在 cookies 的基础上实现的，并且在 cookies 中使用加密的签名。这意味着用户可以查看 cookie 的内容，但是不能修改它，除非它知道签名的密钥。

Flask REST API

一个最小的 API

一个最小的 Flask-RESTful API 像这样

from flask import Flask
from flask.ext import restful

app = Flask(__name__)
api = restful.Api(app)

class HelloWorld(restful.Resource):
    def get(self):
        return {'hello': 'world'}

api.add_resource(HelloWorld, '/')

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

完整的例子

from flask import Flask
from flask_restful import reqparse, abort, Api, Resource

app = Flask(__name__)
api = Api(app)

TODOS = {
    'todo1': {'task': 'build an API'},
    'todo2': {'task': '?????'},
    'todo3': {'task': 'profit!'},
}


def abort_if_todo_doesnt_exist(todo_id):
    if todo_id not in TODOS:
        abort(404, message="Todo {} doesn't exist".format(todo_id))

parser = reqparse.RequestParser()
parser.add_argument('task')


# Todo
# shows a single todo item and lets you delete a todo item
class Todo(Resource):
    def get(self, todo_id):
        abort_if_todo_doesnt_exist(todo_id)
        return TODOS[todo_id]

    def delete(self, todo_id):
        abort_if_todo_doesnt_exist(todo_id)
        del TODOS[todo_id]
        return '', 204

    def put(self, todo_id):
        args = parser.parse_args()
        task = {'task': args['task']}
        TODOS[todo_id] = task
        return task, 201


# TodoList
# shows a list of all todos, and lets you POST to add new tasks
class TodoList(Resource):
    def get(self):
        return TODOS

    def post(self):
        args = parser.parse_args()
        todo_id = int(max(TODOS.keys()).lstrip('todo')) + 1
        todo_id = 'todo%i' % todo_id
        TODOS[todo_id] = {'task': args['task']}
        return TODOS[todo_id], 201

##
## Actually setup the Api resource routing here
##
api.add_resource(TodoList, '/todos')
api.add_resource(Todo, '/todos/<todo_id>')


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

Flask教程