Build a basic flask process

Install virtual environment

python -m venv venv

Insert picture description here
Then run activate and enter the virtual environment;

Install flask in a virtual environment

(venv) pip install flask

Write basic helloworld program

# main.py
from flask import Flask

app = Flask(__name__)


@app.route('/')
def hello_world():
    return "hello world!"

Set FLASK_APP environment variable (windows) and run

(venv) set FLASK_APP=main.py
python -m flask run # 或flask run

After visiting localhost:5000, you can see the returned content.

Basic operation

Bind method to URL

Direct binding

@app.route('/test')
def func():
	return 1

With parameters

@app.route('/test/<variable>')
def func():
	return variable

Processing form data

First introduce the request object (see the concept section)

Manipulate URL parameters, use the args attribute

request.args.get('key')

Operate form-data, use form attribute

request.form['username']

Redirects and errors

Use redirect to redirect requests

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()

Use errorhandler() decorator to decorate the error page

from flask import render_template

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

Operation response (response)

The return value of the view function will be automatically converted into a response object according to certain rules.
Example: The html page (string) returned by not_found will generate a response object with a 404 status code.

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

If a dict is returned, it will be automatically converted to a JSON response

@app.route("/me")
def me_api():
    user = get_current_user()
    return {
    
    
        "username": user.username,
        "theme": user.theme,
        "image": url_for("user_image", filename=user.image),
    }

session与cookies

from flask import Flask,request,session
app = Flask(__name__)
app.secret_key = b'sdafdddd\x]\x'

@app.route('/login', methods=['GET', 'POST'])
def login():
    if request.method == 'POST':
        session['username'] = request.form['username']

Concepts and issues

What is WSGI

WSGI stands for Python Web Server Gateway Interface, which specifies a standard interface between a web server and Python web applications or web frameworks to improve the portability of web applications among a series of web servers
The WSGI standard is that a Web program needs to have a callable object (function) that can accept two parameters. The first parameter is the environ dictionary, and the second parameter is the function called by the callable object to initiate a response.
All the information of the http request can be obtained through environ, and the data of the http response can be used as the body through start_response plus the return value of the function.

def hello(environ, start_response):
    status = "200 OK"
    response_headers = [('Content-Type', 'text/html')]
    start_response(status, response_headers)
    path = environ['PATH_INFO'][1:] or 'hello'
    return [b'<h1> %s </h1>' % path.encode()]

How to handle request

Flask uses the global object request to process client requests.

python flask learning and use