Flash

Flash() provides a very useful flash() function, which can be used to "flash" messages that need to be prompted to the user, such as "welcome back!" when the user logs in successfully. In the view function, call the flash() function to pass in the message content. The flash() function stores the message in the session. We need to use the global function get flash messages() in the template to get the message and display it.

Messages sent through the flash() function are stored in the session object, so we need to set the secret key for the program. You can set it through the app.secret'key property or the configuration variable secret'key.

Source code

def flash(message, category="message"):  # The default category is message
    flashes = session.get("_flashes", [])
    flashes.append((category, message))
    session["_flashes"] = flashes
    message_flashed.send(
        current_app._get_current_object(), message=message, category=category
    )
    
    
def get_flashed_messages(with_categories=False, category_filter=()):
    flashes = _request_ctx_stack.top.flashes
    if flashes is None:
        _request_ctx_stack.top.flashes = flashes = (
            session.pop("_flashes") if "_flashes" in session else []
        )
    if category_filter:
        flashes = list(filter(lambda f: f[0] in category_filter, flashes))
    if not with_categories:
        return [x[1] for x in flashes]
    return flashes

1. Set flash
   • flash("value to be passed", category = "name of classification"), if not, the default is message
     
   • Nature: session ['[flash']
2. Take the value of flash setting, and we use get flash messages
   • get_flashed_messages(with_categories=False, category_filter=())
     • If no category filter is passed, take out the values passed by all categories stored above
     • If you don't pass with categories, only the value will be obtained. If you pass the value, the classification name and classification value will be obtained
       
3. This flash can only be taken from one view function. As long as one view function has been taken, other view functions cannot be taken
   • Essence: session. Pop ("﹐ flash")
     
   • But in the same view function, there are infinite values

case

from flask import Flask,flash,get_flashed_messages,request,redirect

app = Flask(__name__)
app.debug=True
app.secret_key = 'asdfasdf'


@app.route('/index')
def index():
    # Get all the set values from somewhere and clear them.
    #flash('timeout error ', category="x1")
    flash("It's coming. You have to be careful")
    flash("I'm the second",category="ss")
    # return "ssdsdsdfsd"
    return redirect('/error')


@app.route('/error')
def error():
    """
    //Display error messages
    :return:
    //If get ﹐ flashed ﹐ messages (with ﹐ category = true)
    """
    #data = get_flashed_messages(category_filter=['x1'])
    data=get_flashed_messages(with_categories=True,category_filter=['ss'])
    data1 = get_flashed_messages(with_categories=True, category_filter=['ss'])
    print(type(data))
    print(data1)
    return "Error message:%s" %(data,)


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

middleware

The essence is to encapsulate the original execution function

Note: the request extension of Flask is the middleware of Django. Django's middleware is not Flask's Middleware

Custom local Middleware

According to the decorator

from functools import wraps
 
 
def auth(func):
    @wraps(func)
    def inner(*args, **kwargs):
        if not session.get('user'):
            return redirect(url_for('login'))
        ret = func(*args, **kwargs)
        return ret
    return inner
 
@app.route('/login', methods=["GET", "POST"])
@auth
def login():
    return "Sign in"

Custom global decorator

Write in app.py

class Middleware(object):
    
    def __init__(self, old):
        self.old = old
    
    def __call__(self, *args, **kwargs):
        print('Action before request')
        ret = self.old(*args, **kwargs)  
        print('Action after request')
        return ret
 
 
if __name__ == '__main__':
    app.wsgi_app = Middleware(app.wsgi_app)
    app.run()