Why performance matters in Flask - See It in Action

Why performance matters

📖 Scenario: You are building a simple Flask web app that shows a list of products. You want to understand why performance matters by measuring how fast your app responds when users visit the product page.

🎯 Goal: Build a Flask app that stores product data, sets a threshold for slow response, measures the response time for the product page, and adds a message if the response is slow.

📋 What You'll Learn

Create a dictionary called products with exact product names and prices

Add a variable called slow_threshold with the value 0.5 (seconds)

Write a route /products that measures response time and checks if it is slower than slow_threshold

Display the product list and a message if the response is slow

💡 Why This Matters

🌍 Real World

Web apps must respond quickly to keep users happy. Measuring response time helps find slow parts to fix.

💼 Career

Understanding performance is key for web developers to build fast, user-friendly applications.

1

DATA SETUP: Create the product data dictionary

Create a dictionary called products with these exact entries: 'Apple': 1.2, 'Banana': 0.5, 'Cherry': 2.5.

Flask

# Create the products dictionary with exact entries
# Your code here

Need a hint?

Use curly braces to create a dictionary with keys and values.

2

CONFIGURATION: Add a slow response threshold

Add a variable called slow_threshold and set it to 0.5 to represent half a second.

Flask

products = {'Apple': 1.2, 'Banana': 0.5, 'Cherry': 2.5}
# Set slow_threshold to 0.5 seconds
# Your code here

Need a hint?

This variable will help us check if the response is slow.

3

CORE LOGIC: Create the /products route with timing

Write a Flask route for /products that records the start time, renders the product list, calculates the response time, and sets a variable slow_message to "Response is slow" if the response time is greater than slow_threshold, otherwise set it to an empty string.

Flask

products = {'Apple': 1.2, 'Banana': 0.5, 'Cherry': 2.5}
slow_threshold = 0.5

from flask import Flask, render_template_string
import time

app = Flask(__name__)

# Create /products route with timing
# Your code here

Need a hint?

Use time.time() to measure start and end times. Use render_template_string to render HTML with product data and the slow message.

4

COMPLETION: Add the app run command

Add the line app.run(debug=True) at the end of the file to start the Flask app in debug mode.

Flask

products = {'Apple': 1.2, 'Banana': 0.5, 'Cherry': 2.5}
slow_threshold = 0.5

from flask import Flask, render_template_string
import time

app = Flask(__name__)

@app.route('/products')
def show_products():
    start_time = time.time()
    slow_message = ""
    response = render_template_string(
        '''Products
        {% for name, price in products.items() %}
          {{ name }}: ${{ price }}
        {% endfor %}
        {{ slow_message }}''',
        products=products, slow_message=slow_message
    )
    response_time = time.time() - start_time
    if response_time > slow_threshold:
        slow_message = "Response is slow"
    return render_template_string(
        '''Products
        {% for name, price in products.items() %}
          {{ name }}: ${{ price }}
        {% endfor %}
        {{ slow_message }}''',
        products=products, slow_message=slow_message
    )

# Add the app run command below
# Your code here

Need a hint?

This line starts the Flask app so you can visit it in your browser.