Flask - Variable Rule

Last Updated : 29 May, 2026

Flask variable rules are used to create dynamic URLs by capturing values directly from the URL. These values are passed to the view function and can be used to display different content based on user input. Rules for Variable Parts in Routes:

  • Variables are defined using <variable_name> inside the route.
  • Captured values are passed as arguments to the view function.
  • Converters like <int:id> and <string:name> can be used to specify the data type of the variable.

Dynamic URLs Variable

The following converters are available in Flask-Variable Rules:

  • string accepts any text without a slash (default).
  • int accepts only integers.
  • float like int but for floating point values.
  • path like the default but also accepts slashes.
  • any matches one of the items provided.
  • UUID accepts UUID strings.

Example: In this code, a basic flask app is created in which return a welcome line.

Python 
from flask import Flask
app = Flask(__name__)

@app.route('/')
def msg():
    return "Welcome To The GeeksforGeeks"

app.run(debug=True)

Output Run the app by executing this command in the terminal "python app.py".

Screenshot-2026-05-21-105445
Output

String Variable

In this code, we will define a function that handles a dynamic string variable in the URL.

Python 
from flask import Flask
app = Flask(__name__)

@app.route('/')
def msg():
    return "Welcome"

@app.route('/vstring/<name>')
def string(name):
    return "My Name is %s" % name

app.run(debug=True)

Output

Screenshot-2026-05-21-105702
Output
Screenshot-2026-05-21-105725
Output

Explanation:

  • @app.route('/') defines the homepage route that returns a welcome message.
  • @app.route('/vstring/<name>') dynamic route that takes a string parameter and displays it in a message.
  • app.run(debug=True) runs the Flask app with debugging enabled.

Integer Variable

This create a function that handles integers since Flask doesn't define it by default. Finally, we return the integer value and run the app. To access the integer page, we include the function name and an integer in the URL.

Python 
from flask import Flask
app = Flask(__name__)

@app.route('/')
def msg():
    return "Welcome"

@app.route('/vint/<int:age>')
def vint(age):
    return "I am %d years old " % age

app.run(debug=True)

Output

Integer-Variable-Flask
Integer Variable Flask

Explanation: vint() function handles URLs with an integer parameter (<int:age>) which ensures only integers are accepted and returns a formatted string with the provided age.

Float Variable

Here, we define a float function since Flask doesn’t define it by default. The function returns the float value and we run the app using Flask run. To access the float page, we include the function name and a floating-point number in the URL.

Python 
from flask import Flask
app = Flask(__name__)

@app.route('/')
def msg():
    return "Welcome"

@app.route('/vfloat/<float:balance>')
def vfloat(balance):
    return "My Account Balance %f" % balance

app.run(debug=True)

Output

Flask - Variable Rule
Float Variable

Explanation: vfloat function handles URLs with a float value (e.g., /vfloat/100.50). It returns a formatted message displaying the float value.

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