1 Quick Start | Flask开发

运行¹

如果是.py文件，使用下面的语句：

$ set FLASK_APP=hello.py
$ flask run

如果是文件夹，则为：

$ set FLASK_APP=hello
$ flask run

如果使用调试模式，在flask run前添加：

$ set FLASK_ENV=development

使服务器对外可见

Externally Visible Server If you run the server you will notice that
the server is only accessible from your own computer, not from any
other in the network. This is the default because in debugging mode a
user of the application can execute arbitrary Python code on your
computer.

If you have the debugger disabled or trust the users on your network,
you can make the server publicly available simply by adding
–host=0.0.0.0 to the command line:

$ flask run --host=0.0.0.0 This tells your operating system to listen
on all public IPs.

更多信息

关于部署，可以参考Deployment Options。
开发服务器的更多参数在Development Server。
关于调试器，可以参考Werkzeug documentation。

路由

使用route()装饰器来将函数绑定到URL上。

@app.route('/xxx/<var>')
def func():
	return 'hello'

URL可以是动态的。<var>中的内容可以被用作参数，对其类型转换的操作如下。

类型转换

使用<converter:variable_name>来指定参数的类型。可指定的类型如下表：

type	description
string	(default) accepts any text without a slash
int	accepts positive integers
float	accepts positives floating point values
path	like string but also accepts slashes
uuid	accepts UUID strings

url_for()

使用url_for()来将一个指向一个函数的URL。

也可以通过下面的方式指向一个静态文件。静态文件存放在static文件夹中，并作为url_for的endpoint参数。

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

HTTP方法

通常情况下，路由回应GET request。在app.route()中添加methods参数来处理不同的HTTP方法。例如：

from flask import request

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

Render Templates

使用render_template()方法来渲染一个template。可以将参数传递给template；template之间的继承在保持风格的同时也减少了代码量。

from flask import render_template

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

关于template的更多信息可参考Jinja2。

参数可以通过下面的方式从函数传递给template：

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

在template可以获取request，session和g的对象信息，以及get_flashed_messages()函数。

Accessing Request Data

在flask中，客户端向服务器端发送的数据由全局对象request²回应。flask中使用Context Locals³来实现“全局对象” (测试或单元测试时需查阅)。

通过request对象的method⁴ 属性来获取当前request的method。通过form⁵ 属性来从POST或PUT请求访问数据。

from flask import request

@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 is executed if the request method
    # was GET or the credentials were invalid
    return render_template('login.html', error=error)

File Uploads

在HTML中设置：

enctype="multipart/form-data"

少量的信息在Quickstart中，更多信息在Uploading Files Pattern中。

Cookies

待更新
https://flask.palletsprojects.com/en/1.1.x/quickstart/#cookies

Redirects and Errors

from flask import abort, redirect, url_for

@app.route('/')
def index():
	# to redirect a user to another endpoint, use the redirect() function
    return redirect(url_for('login'))

@app.route('/login')
def login():
	# to abort a request early with an error code, use the abort() function
    abort(401)
    this_is_never_executed()

如果想要修改错误页，使用errorhandle()装饰器。

from flask import render_template

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

Sessions

session在多个request的处理过程中存储当前的用户信息。

This is implemented on top of cookies for you and signs the cookies cryptographically. What this means is that the user could look at the contents of your cookie but not modify it, unless they know the secret key used for signing.

使用session需要设置一个secret key。

from flask import Flask, session, redirect, url_for, request
from markupsafe import escape

app = Flask(__name__)

# Set the secret key to some random bytes. Keep this really secret!
app.secret_key = b'_5#y2L"F4Q8z\n\xec]/'

@app.route('/')
def index():
    if 'username' in session:
        return 'Logged in as %s' % escape(session['username'])
    return 'You are not logged in'

@app.route('/login', methods=['GET', 'POST'])
def login():
    if request.method == 'POST':
        session['username'] = request.form['username']
        return redirect(url_for('index'))
    return '''
        <form method="post">
            <p><input type=text name=username>
            <p><input type=submit value=Login>
        </form>
    '''

@app.route('/logout')
def logout():
    # remove the username from the session if it's there
    session.pop('username', None)
    return redirect(url_for('index'))

The escape() mentioned here does escaping for you if you are not using the template engine (as in this example).

使用下面的方法生成一个好的secret key。

$ python -c 'import os; print(os.urandom(16))'
b'_5#y2L"F4Q8z\n\xec]/'

Message Flashing

The flashing system basically makes it possible to record a message at the end of a request and access it on the next (and only the next) request. This is usually combined with a layout template to expose the message.

To flash a message use the flash() method, to get hold of the messages you can use get_flashed_messages() which is also available in the templates. Check out the Message Flashing for a full example.

Logging

The attached logger is a standard logging Logger, so head over to the official logging docs for more information.

Read more on Application Errors.

Using Flask Extensions

Extensions are packages that help you accomplish common tasks. For example, Flask-SQLAlchemy provides SQLAlchemy support that makes it simple and easy to use with Flask.

For more on Flask extensions, have a look at Extensions.

Deploying to a Web Server

Deployment Options

未包含部分

• About Responses
• Hooking in WSGI Middleware

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1. Quickstart ↩︎

2. Request ↩︎

3. Context Locals ↩︎

4. request.method ↩︎

5. request.form ↩︎