Timezones: A timezone converter

A small Flask web app that converts one or more input times into multiple time zones (by IANA timezone ID or city/place name). City/place lookups are resolved server-side on submit using a geocoder + GeoNames timezone service.

Example version running on render at: https://timezones-5d1h.onrender.com

Features

• Convert multiple input times at once.
• Enter targets as either IANA timezone IDs (e.g. America/Los_Angeles) or place names (e.g. San Francisco, CA).
• Minimal JavaScript UI with add/remove inputs and datalist autocompletion.
• Server-side city → timezone resolution (Nominatim geocoding + GeoNames timezone lookup).

How to Use the App

1. Enter one or more times in the first set of boxes (the app accepts YYYY-MM-DD HH:MM or similar ISO-like inputs, or use the date picker).
2. Choose a base timezone (you can type to filter) — this is the timezone of the input times.
3. Add one or more target entries in the second set of boxes; each target can be either an IANA timezone (e.g., Europe/London) or a city/place name (e.g., Mumbai, India).
4. Submit the form to see a grid of converted times. Each cell shows the converted date/time in that timezone.

Tips:

• Use an exact IANA timezone ID when possible for predictable results.
• If a place lookup is ambiguous, try adding a region/country (e.g., Springfield, IL vs Springfield, MA).

Quick Start

Note: If you started codespaces with the button above, you can skip to step 3

1. Create and activate a virtual environment:

python -m venv .venv
source .venv/bin/activate

2. Install dependencies:

pip install -r requirements.txt

3. Set environment variables and run the app (Unix/macOS):

export FLASK_APP=app.py
export FLASK_ENV=development
export GEONAMES_USERNAME=your_geonames_username
flask run

On Windows (PowerShell):

$env:FLASK_APP = 'app.py'
$env:FLASK_ENV = 'development'
$env:GEONAMES_USERNAME = 'your_geonames_username'
flask run

3. Alternative: you can also run the app with

export GEONAMES_USERNAME=your_geonames_username
python app.py

Open http://127.0.0.1:5000/ in your browser.

Geonames & City Lookup

The app uses two free services to resolve place names to timezones:

• Nominatim (OpenStreetMap) for geocoding (place → lat/lon).
• GeoNames timezoneJSON service for lat/lon → IANA timezone.

GeoNames requires a username. Create a free account at https://www.geonames.org/ and set the GEONAMES_USERNAME environment variable before running the app. You'll also need to activate the free API on your account. The app will fall back to the GeoNames demo username if you don't set one, but that account is strictly rate-limited and not suitable for production.

Notes and best practices:

• Respect Nominatim's usage policy: do not bulk-query their service and add a sensible delay or caching for repeated lookups. See https://operations.osmfoundation.org/policies/nominatim/.
• Use your own GeoNames username to avoid the demo quota.

Project Structure

• app.py: Flask application (routes, form handling)
• conversions.py: timezone and city-resolution logic, time conversion.
• templates/index.html: Main page with the input form and inline results.
• requirements.txt: Python dependencies.
• requirements_dev.txt: Python dependencies for testing.
• tests/: Pytest tests.
• documents/: markdown files with documents for the Smarter Software Testing course
• README.md: This file.

Troubleshooting

• Time format issues: the app expects reasonably parseable datetimes. If your input is rejected or parsed incorrectly, try using full YYYY-MM-DD HH:MM format.
• Unrecognized timezone: If you enter an invalid timezone ID you'll see an "Unrecognized timezone" message in results. Use an IANA timezone ID (see the Olson database, for example https://en.wikipedia.org/wiki/List_of_tz_database_time_zones) for best results.
• City lookup failures: If a place name doesn't resolve, try these steps:
  • Add more context (city, state/province, country).
  • Confirm GEONAMES_USERNAME is set and valid.
  • Check network connectivity and that external services are reachable.
  • Consider switching to a timezone ID directly to bypass geocoding.
• Rate limiting: If many lookups are done in a short time you may hit Nominatim or GeoNames rate limits. Add caching, batch requests, or run fewer queries during development.

Running Tests

Install the test extras in requirements_dev.txt and run:

pytest

Tests should mock external HTTP calls so they should run without network access.

Notes for Deploying / Production

• Replace the demo GeoNames username with your own and implement caching for geocoding results.
• If you expect heavy traffic, set up a private geocoding/timezone service or use a commercial provider to avoid rate limits.
• Serve the Flask app with a production WSGI server (Gunicorn / uWSGI) behind a reverse proxy.