047-amazon-price-tracker/README.md

🚀 Amazon Price Tracker

A Python bot for Day 47 of Udemy's "100 Days of Code: The Complete Python Pro Bootcamp": it reads a product page, extracts the price and sends an e-mail alert when the price drops below a target. Made for course participants who want to compare solutions and for visitors who browse for ideas.

📚 Table of Contents

• Overview
• Requirements
• Setup
• Run
• Tests
• License
• Links
• Appendix: Project documents

🧭 Overview

The assignment is built in four lecture steps. Each step was delivered on its own branch and pull request, and each has a screenshot and a wiki page in English, Danish and Bahasa Malaysia that explains what it teaches.

Step	What it adds	Status
1	Scrape the price from the practice page with BeautifulSoup	done
2	E-mail alert below the target price, secrets in .env	done
3	Browser-like request headers	done
4	The live Amazon page	done (Amazon answers with a robot check, see below)

Step 1: scrape the price

get_title(html) and get_price(html) in src/amazon_price_tracker/infrastructure/scraper.py use BeautifulSoup on the practice page. The price element has the class a-offscreen and its text is $99.99; split("$") removes the currency sign and float() returns 99.99.

Step 2: e-mail alert below the target

check_price in src/amazon_price_tracker/application/alert.py compares the price with TARGET_PRICE (100) from constants.py. When it is lower, SmtpNotifier (infrastructure/mailer.py) connects to your SMTP server on port 587, starts TLS, logs in and sends a message with the title, the price and the link to buy. The SMTP address, e-mail address and password come from your own .env through python-dotenv, so they never appear in the code. The practice page costs 99.99, so a target of 100 triggers the alert.

The screenshots below come from a run where the SMTP connection is replaced by a recording stub, so no mail is sent; the second image is rendered from the message the code builds.

Step 3: request headers

A browser sends headers with every request: the browser and system (User-Agent), the preferred language (Accept-Language) and more. A bare script sends almost none, so a server can answer in the wrong language or currency, or treat the request as a bot. DEFAULT_HEADERS in constants.py holds the browser-like set (without Host and X-Amzn-Trace-Id, as the lecture says) and RequestsPageFetcher passes it as headers= to requests.get.

What a browser sends to httpbin.org/headers, and what the bot sends (Host is added by requests itself):

Step 4: the live Amazon page

The default product is the lecture's Amazon page (AMAZON_URL in constants.py). On 2026-10-28 the bot asked for it with the Step 3 headers and Amazon answered HTTP 200 with a robot-check page ("Click the button below to continue shopping") instead of the product, so there was no price to read. This is the outcome the lecture warns about: live pages change and Amazon may refuse scripts.

The bot recognises that page (is_robot_check in infrastructure/scraper.py), stops with a clear message and does not try to solve or get past the check. The price and title selectors are listed in constants.py (PRICE_SELECTORS, TITLE_SELECTORS), so they are easy to change when Amazon changes its markup. Set PRODUCT_URL in your .env to track another page, for example the practice page https://appbrewery.github.io/instant_pot/, where Steps 1 to 3 work.

Repository layout:

Path	What it is for
src/amazon_price_tracker/	The package; constants.py is the only place for constants
tests/	pytest tests; they never use the network or a real mail server
docs/	Project documents (Business Case, plan, milestones, reviews) and the wiki pages
Doxyfile	Doxygen configuration for the source comments
.env.example	The settings you put in your own .env

📋 Requirements

• Python 3.13 or newer.
• Runtime packages (installed by pip): requests, beautifulsoup4, python-dotenv. Nothing else is needed to run the bot.
• Optional, for development: pytest, ruff, mypy (the dev extra) and Doxygen for the API documentation.

🛠️ Setup

Create a local virtual environment named .venv, activate it and upgrade pip:

python -m venv .venv

Activate it (Linux and macOS):

source .venv/bin/activate

Activate it (Windows PowerShell):

.venv\Scripts\Activate.ps1

Activate it (Windows Git Bash):

source .venv/Scripts/activate

Upgrade pip and install the project with the development tools:

python -m pip install --upgrade pip

python -m pip install -e ".[dev]"

For use without development tools, install with python -m pip install -e ..

Create your own settings file from the example and fill in the values. .env is ignored by git; never commit it:

cp .env.example .env

Gmail needs 2-Step Verification and an App Password; use the App Password as EMAIL_PASSWORD. SMTP addresses: Gmail smtp.gmail.com, Hotmail smtp.live.com, Outlook outlook.office365.com, Yahoo smtp.mail.yahoo.com. The bot connects on port 587.

▶️ Run

Fill in your .env first (see Setup), then start the bot. It reads the product at PRODUCT_URL (the Amazon page unless you set another one), prints the title and the price and sends the alert when the price is below the target. Amazon currently answers with a robot check, so to see the alert work set PRODUCT_URL="https://appbrewery.github.io/instant_pot/" in .env:

python -m amazon_price_tracker

🧪 Tests

python -m pytest

Lint and type checks:

ruff check .

mypy

Build the API documentation (written to docs/doxygen/, which is git-ignored):

doxygen Doxyfile

📄 License

GNU Affero General Public License v3.0, see LICENSE.

🔗 Links

• Repository
• Documentation
• Issue tracker
• Wiki in English, Danish and Bahasa Malaysia (what we gained in each lecture step; the pages are in docs/wiki/)

📎 Appendix: Project documents

The documents a newcomer needs, in reading order.

Document	What it tells you
AGENTS.md	The rules AI agents follow in this repository
Business Case	Why the project exists, its scope and success criteria
Stakeholder Analysis	Who is involved; the stakeholder IDs used for owners and reviewers
Project Plan	The gateways and their schedule
Milestones	One document per gateway: Go/No-Go criteria and tasks
Artifact registry	Where each artifact type lives, the next version, the PO language and domain
Framework README	The framework this project uses
Framework changelog	What changed in each framework release

---