When you click on an extension button in Chrome, the browser gets geolocation and sends it by HTTP to server.py. The server makes a request to Google Maps Geocoder to get address from these coordinates. When geocoding is completed, the server saves data with your location to Google Spreadsheets: Longitude, Latitude, Date, City, and Country.
I used developers guide to get started with Chrome Extension. This script is only 25 lines of code, it gets geolocation and sends it to local server.
Why do you need a local server and why can't you just send coordinates directly to Google SpreadSheets from the browser? First of all you need to authorize in Google Apps, and you can't do it directly from Chrome Extension. Then you would also need to geocode the coordinates and doing it from extension would be tricky. So I decided to build a local server in Python and keep it running on my Macbook all the time.
The server does all the work. It reads coordinates from HTTP request and sends a request to Google Maps Geocoder. Then it extracts "city" and "country" fields from the geocoding result. To avoid duplicates in the sheet, the server gets the last row from the spreadsheet and compares it with the current data. If the last row is different, the server inserts a new row with Longitude, Latitude, Date, City, Country. If the data has been saved correctly it responds with HTTP 200 OK and "Saved!" as response body.