Back-end Web Framework: Flask (Part-2: Routing & URL Binding)
Web frameworks nowadays use the routing technique to help users to navigate through a web without having to remember application URLs. It is useful to access the desired page directly without having to navigate from the home page.
from flask import Flask
app = Flask(__name__) @app.route('/')
def index():
return 'This is homepage' @app.route('/about')
def about():
return '<h2> About page </h2>'
if __name__ == "__main__":
app.run(debug = True)
Route() decorator can be used to inject additional functionality to one or more functions.
app.route(rule, option) Rule represents the URL binding with the function and option is a list of parameters to be forwarded to the underlying Rule options.
@app.route(‘/’) This is the URL and whenever a client requests it the server will send back the return value i.e. return ‘This is homepage’ . Now, suppose we want to go to the about page, then we write this @app.route(‘/about’) . This returns return ‘<h2> About page </h2>’ . We can also put HTML codes in the return statement. def index(): and def about(): are functions.
app.run(host, port, debug, option) But we just use the debug in this example. host defaults to 127.0.0.1 (localhost)and Sets to ‘0.0.0.0’ to have server available externally
port defaults to 5000
debug defaults to false. If set to true, provides a debug information
options forwards to underlying Werkzeug server.
app.run(debug = True) when the app is under development, it should be restarted manually for each change in the code. To avoid this inconvenience, we enable the debug mode. The server then will reload itself with any changes in code. It’s also useful when there is a bug in the code and helps find errors.
There is url_for function which is very useful if we want a dynamically build URL.
from flask import Flask
app = Flask(__name__)@app.route('/teacher')
def hello_teacher():
return 'Hey Teacher'@app.route('/students/<student>')
def hello_students(student):
return 'Hello %s as student' %student@app.route('/user/<name>')
def hello_user(name):
if name == 'teacher':
return redirect(url_for('hello_teacher'))
else:
return redirect(url_for('hello_students'))if __name__ == "__main__":
app.run(debug = True)
This is a dynamic URL example
@app.route('/user/<name>) This here suggests the variable part <name> , it takes in any variable name and displays it later. If ‘teacher’ is supplied to def hello_user(name): function as argument. The hello_user() function checks if an argument received matches ‘teacher’ or not. If it matches, the application is redirected to the hello_teacher() function using url_for(), otherwise to the hello_students() function passing the received argument as guest parameter to it.
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