First experience of flask

flask First experience

preparation

Creating a virtual environment

mkdir myproject
cd myproject
python3 -m venv venv

Activate the virtual environment

. venv/bin/activate

install Flask

pip3 install Flask

One of the simplest applications

from flask import Flask

app = Flask(__name__)


@app.route('/')
def hello_world():
    return '<p>Hello World!</p>'


if __name__ == '__main__':
    ''' :param host:  Specify listening host , The default is 127.0.0.1(localhost),  Set up 0.0.0.0  Run any network access  :param port:  Specify exposure port , Default usage port 5000 :param debug:  The default is false.  If set to true, Provides debugging information  :param options:  To forward to the bottom Werkzeug The server . '''
    app.run(debug=True)

route

modern web Applications use meaningful URL , This helps users remember , Web pages will be more favored by users , Improve the return rate .

Use route() Decorator to bind functions to URL:

from flask import Flask

app = Flask(__name__)


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


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

Variable rule

Flask Variable rule

Through the URL Part of the is marked as <variable_name> You can go to URL Add variables to .

Of the tag Part will be passed to the function as a keyword parameter .

By using converter:variable_name , Sure Selectively add a converter , Specify rules for variables

from markupsafe import escape
from flask import Flask

app = Flask(__name__)


@app.route('/user/<username>')
def show_user_profile(username):
    # show the user profile for that user
    return f'User {
      escape(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 f'Post {
      post_id}'


@app.route('/path/<path:subpath>')
def show_subpath(subpath):
    # show the subpath after /path/
    return f'Subpath {
      escape(subpath)}'

Converter type

type	describe
string	( The default value ) Accept any text without slashes
int	Accept positive integers
float	Accept a positive floating point number
path	similar string, But it can contain slashes
uuid	Accept UUID character string

HTML escape

When to return to HTML （ Flask The default response type in ） when , To prevent injection attacks , All users The value supplied must be escaped before output rendering . Use Jinja Rendered HTML The template will do this automatically .

Manual escape

from markupsafe import escape
from flask import Flask

app = Flask(__name__)


@app.route("/<name>")
def hello(name):
    return f"Hello, {
      escape(name)}!"

Flask URL structure

url_for() Functions are important for building specific functions dynamically URL Very useful .

url_for() The function takes the name of the function as the first argument , And one or more keyword parameters , Each parameter corresponds to URL The variable part of

from flask import Flask, redirect, url_for

app = Flask(__name__)


#  Use redirect  and url_for  To jump 

@app.route('/admin')
def hello_admin():
    return 'Hello admin'


@app.route('/guset/<guset>')
def hello_guset(guset):
    return f'Hello {
      guset} as Guset'


@app.route('/user/<name>')
def show_name(name):
    if name == 'admin':
        return redirect(url_for('hello_admin'))
    else:
        return redirect(url_for('hello_guset', guset=name))


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

show_name Function to check whether the received parameter is consistent with 'admin’ Match , If matching url_for() Redirect the app to hello_admin() Go to , Otherwise, the part parameter is taken as guset Pass to hello_guset() function .

FLASK HTTP Method

• Http Protocol is the basis of data communication in the world wide web . Defined in the protocol from the specified URL Different ways to retrieve data .

• Method	describe
  GET	Send data to the server in an unencrypted form . The most common method .
  HEAD	and GET In the same way , But there's no responder .
  POST	Is used to HTML The form data is sent to the server .POST Method is not cached by the server .
  PUT	Replace all current representations of the target resource with the uploaded content .
  DELETE	Delete from URL All current representations of the given target resource .

  Create one under the path login.html

  <html>
  <head>
      <meta charset="utf-8"/>
      <title>Flask HTTP Request method processing </title>
  </head>
     <body>
        <form action = "http://localhost:5000/login" method = "post">
           <p> Enter a name :</p>
           <p><input type = "text" name = "name" value=""/></p>
           <p><input type = "submit" value = " Submit " /></p>
        </form>
  
     </body>
  </html>
  

  python Enter the following script

  
  from flask import Flask, redirect, url_for, request
  
  app = Flask(__name__)
  
  
  @app.route('/success/<name>')
  def success(name):
      return 'welcome %s' % name
  
  
  @app.route('/login', methods=['POST', 'GET'])
  def login():
      if request.method == 'POST':
          user = request.form['name']
          return redirect(url_for('success', name=user))
      else:
          user = request.args.get('name')
          return redirect(url_for('success', name=user))
  
  
  if __name__ == '__main__':
      app.run(debug=True)
  

  start-up flask service , take login.html Drag and drop into the browser to open , Input and submit , You will see that you are transferred to flask success() Function

  
  The above is the use of Flask A simple record of