How to Generate and Read QR Codes with Python: A Step‑by‑Step Guide

What is a QR code?

QR codes are machine‑readable two‑dimensional barcodes that can store various kinds of information. They were invented in 1994 by Masahiro Hara of Denso Wave to track automotive parts and became popular in the late 2010s as smartphones added built‑in scanners. Today they are used for payments, menus, Wi‑Fi passwords, product details, and more.

In this article we will learn how to generate and read QR codes using Python.

Generating QR Codes

First, install the qrcode package: pip install qrcode Simple QR code example:

# Import library
import qrcode
# Generate QR code
img = qrcode.make('Hello World')
img.save('hello.png')

Note: Do not scan random QR codes with your phone, as they may contain malicious links or code.

Advanced QR Codes

The QRCode object allows customization via several parameters:

version : Controls the size of the code (1–40). Version 1 creates a 21×21 matrix.

error_correction : Determines error‑correction level (L 7%, M 15%, Q 25%, H 30%).

box_size : Number of pixels for each box.

border : Thickness of the border (default 4).

Key methods of the QRCode object:

add_data : Add the data to encode.

make : Build the QR matrix; set fit=True to let the library choose the optimal version.

make_image : Render the QR code as an image; fill_color and back_color can customize colors.

Advanced example (creates a red QR code on a black background pointing to a Medium profile):

qr = qrcode.QRCode(
    version=1,
    error_correction=qrcode.constants.ERROR_CORRECT_L,
    box_size=10,
    border=4,
)
qr.add_data("https://abhijithchandradas.medium.com/")
qr.make(fit=True)
img = qr.make_image(fill_color="red", back_color="black")
img.save("medium.png")

Reading QR Codes

Install OpenCV if it is not already present: pip install cv2 Use OpenCV’s QRCodeDetector to decode a QR image:

import cv2
img = cv2.imread("medium.png")
det = cv2.QRCodeDetector()
val, pts, st_code = det.detectAndDecode(img)
print(val)  # prints the encoded URL

The detectAndDecode function returns the decoded text, the corner points of the QR code, and a binarized version of the QR image.