How can I get the named parameters from a URL using Flask?

Use request.args to get parsed contents of query string:

from flask import request

@app.route(...)
def login():
    username = request.args.get('username')
    password = request.args.get('password')

The URL parameters are available in request.args, which is an ImmutableMultiDict that has a get method, with optional parameters for default value (default) and type (type) - which is a callable that converts the input value to the desired format. (See the documentation of the method for more details.)

from flask import request

@app.route('/my-route')
def my_route():
  page = request.args.get('page', default = 1, type = int)
  filter = request.args.get('filter', default = '*', type = str)

Examples with the code above:

/my-route?page=34               -> page: 34  filter: '*'
/my-route                       -> page:  1  filter: '*'
/my-route?page=10&filter=test   -> page: 10  filter: 'test'
/my-route?page=10&filter=10     -> page: 10  filter: '10'
/my-route?page=*&filter=*       -> page:  1  filter: '*'

You can also use brackets <> on the URL of the view definition and this input will go into your view function arguments

@app.route('/<name>')
def my_view_func(name):
    return name

If you have a single argument passed in the URL you can do it as follows

from flask import request
#url
http://10.1.1.1:5000/login/alex

from flask import request
@app.route('/login/<username>', methods=['GET'])
def login(username):
    print(username)

In case you have multiple parameters:

#url
http://10.1.1.1:5000/login?username=alex&password=pw1

from flask import request
@app.route('/login', methods=['GET'])
    def login():
        username = request.args.get('username')
        print(username)
        password= request.args.get('password')
        print(password)

What you were trying to do works in case of POST requests where parameters are passed as form parameters and do not appear in the URL. In case you are actually developing a login API, it is advisable you use POST request rather than GET and expose the data to the user.

In case of post request, it would work as follows:

#url
http://10.1.1.1:5000/login

HTML snippet:

<form action="http://10.1.1.1:5000/login" method="POST">
  Username : <input type="text" name="username"><br>
  Password : <input type="password" name="password"><br>
  <input type="submit" value="submit">
</form>

Route:

from flask import request
@app.route('/login', methods=['POST'])
    def login():
        username = request.form.get('username')
        print(username)
        password= request.form.get('password')
        print(password)