Quickstart

Quickstart

Installation

pip install flask

---

Minimal app

Code Here ⚙️

from flask import Flask

app = Flask(__name__)

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

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

So what did that code do?

1. First we imported the Flask class. An instance of this class will be our WSGI application.

2. Next we create an instance of this class. The first argument is the name of the application’s module or package. name is a convenient shortcut for this that is appropriate for most cases. This is needed so that Flask knows where to look for resources such as templates and static files.

3. We then use the route() decorator to tell Flask what URL should trigger our function.

4. The function returns the message we want to display in the user’s browser. The default content type is HTML, so HTML in the string will be rendered by the browser.

---

Debug Mode

Code Here ⚙️

from flask import Flask

app = Flask(__name__)

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

# debud mode running on 8000 port
if __name__=="__main__":
    app.run(debug=True, port=8000)

The flask run command can do more than just start the development server. By enabling debug mode, the server will automatically reload if code changes, and will show an interactive debugger in the browser if an error occurs during a request.

Warning ⚠️ The debugger allows executing arbitrary Python code from the browser. It is protected by a pin, but still represents a major security risk. Do not run the development server or debugger in a production environment.

---

Routing

Code Here ⚙️

from flask import Flask

app = Flask(__name__)

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

@app.route('/login')
def login():
    return 'This is Login Page'

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

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

Modern web applications use meaningful URLs to help users. Users are more likely to like a page and come back if the page uses a meaningful URL they can remember and use to directly visit a page.

Use the route() decorator to bind a function to a URL.

---

Url Variables

Code Here ⚙️

  
from flask import Flask, render_template

app = Flask(__name__)

@app.route('/')
def index():
    return render_template('index.html')

# string
@app.route('/string/<string:value>')
def string(value):
    return f"<p>Hi this is a string value {value}</p>"

# int
@app.route('/int/<int:value>')
def int(value):
    return f"<p>Hi this is a int value {value}</p>"

# float
@app.route('/float/<float:value>')
def float(value):
    return f"<p>Hi this is a float value {value}</p>"

# path
@app.route('/path/<path:value>')
def path(value):
    return f"<p>Hi this is a path value {value}</p>"

# uuid
@app.route('/uuid/<uuid:value>')
def uuid(value):
    return f"<p>Hi this is a uuid value {value}</p>"



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

You can add variable sections to a URL by marking sections with <variable_name>. Your function then receives the <variable_name> as a keyword argument. Optionally, you can use a converter to specify the type of the argument like converter:variable_name.

Type	Value	Use
string	(default) accepts any text without a slash	string:value
int	accepts positive integers	int:value
float	accepts positive floating point values	float:value
path	like string but also accepts slashes	path:value
uuid	accepts UUID strings	uuid:value