Tracking Amazon Prices for Free

The Problem:

I want to be notified when a product on Amazon goes down in price. But the websites that do offer this service require $$ or have lots of restrictions.

The Plan:

1. Program a Python script that continuously tracks a webpage for any price changes
2. Add a feature to be notified through a GroupMe chat bot.
3. Have the program run on a Google Cloud Computing server for free
4. Save $$

Python Programming:

We’re going to need a few things first.

1. A good text editor. I’d recommend Visual Studio Code (VSC)
2. If you are not on a MacOS computer, download Python3
3. Download the Python extension for VSC
4. In the terminal window in VSC, type pip install selenium
5. Download the chrome webdriver: here
6. Unzip the file, and you should be good to go. If there are any problems on windows follow this guide

In order to track the elements on a website, we will be using Selenium & the ChromeDriver, but there are other options like bs4. 

Create a new python file. It can be named anything, but just make sure you have the .py extension at the end

ex. amazon_price.py

Importing Libraries:

import requests
from selenium import webdriver
import selenium as se
from selenium.common.exceptions import NoSuchElementException  
import time
from time import sleep
from random import randint

Setting Up Chrome Driver:

options = se.webdriver.ChromeOptions()

chrome is set to headless

options.add_argument('headless')

driver = se.webdriver.Chrome(options=options)

Getting the Web Page & Price:

Place Amazon product you want to track

driver.get("https://www.amazon.com/Sony-Noise-Cancelling-Headphones-WH1000XM3/dp/B07G4MNFS1/ref=sr_1_2?crid=N5OCS4NJDH4M&keywords=sony+wh-1000xm3&qid=1551040801&s=gateway&sprefix=sony+%2Caps%2C120&sr=8-2")

sets base price once

global_base_price = driver.find_element_by_xpath('//*[@id="priceblock_ourprice"]').text

Creating Check Changes Function:

def check_change_by_xpath(xpath, base_price):
    try:
        # refreshes the page, finds the price
        # if the price changed, the current price is returned
        driver.refresh
        current_price = driver.find_element_by_xpath('//*[@id="priceblock_ourprice"]').text
        if current_price != base_price:
            return current_price
    except requests.exceptions.RequestException as e:
        sleep(60)
    return False

The Loop:

while True:
    current_state = check_change_by_xpath('//*[@id="priceblock_ourprice"]', global_base_price)
    print("curr state ", current_state)
    if current_state != False:
        global_base_price = current_state
    sleep(randint(3,5))

Now we’re done writting the Python script, let’s try running it!

In terminal, python3 name_of_file.py

If everything worked out with no errors, lets move on to getting GroupMe setup.

GroupMe:

Go to the GroupMe dev page here, and have a Groupme account and make a group with only you in it.\

1. Click on the Bots tab -> login -> Create Bot 
2. Select a group, name the bot something, and you can leave the other fields blank

3. copy the bot id and you can copy and paste it into the code below: 

   post_params = { 'bot_id' : 'insert_botID_here', 'text': "your string response" }
       requests.post('https://api.groupme.com/v3/bots/post', params = post_params)

4. Place the cope snippet anywhere you want to send a message to your phone

Now Your Done!!!

For my version of the finished product go to my github repository