Status of Last Deployment:

💱 Exchange Rate Web Application

A practical assignment for the Python Advanced course.

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Task

• Develop an asynchronous microservice to get the exchange rate of a given currency against a fixed set of target currencies.
• Add support for specifying a date in the request.
• Store cache on disk to reduce unnecessary API calls.

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Description

Libraries

• Use aiohttp server to create the asynchronous web application.
• Use aiohttp client for making asynchronous network requests.
• Use aiofiles to work with files asynchronously (read/write).

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API

You can use any public API to retrieve exchange rates.

A free option: fawazahmed0/currency-api

• ✅ List of available currencies:
  https://cdn.jsdelivr.net/npm/@fawazahmed0/currency-api@latest/v1/currencies.json

• ✅ Exchange rate for a given currency (latest):
  https://cdn.jsdelivr.net/npm/@fawazahmed0/currency-api@latest/v1/currencies/{currency}.json
  Example: https://cdn.jsdelivr.net/npm/@fawazahmed0/currency-api@latest/v1/currencies/eur.json

• ✅ Exchange rate for a given currency on a specific date:
  Replace latest with a date in ISO-8601 format:
  https://cdn.jsdelivr.net/npm/@fawazahmed0/currency-api@{date}/v1/currencies/{currency}.json
  Example: https://cdn.jsdelivr.net/npm/@fawazahmed0/currency-api@2024-09-28/v1/currencies/rub.json

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Configuration

• Define a static list of target currencies to which the exchange rate should be returned.

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API Wrapper

Create a wrapper for handling API requests:

• Use aiohttp client for network communication.
• Implement a high-level method to fetch the exchange rate for a selected currency and date.
• Add a method to read from cache (disk).
• If a cached value exists for the currency and date — return it without making network requests.
• On the first API call, build a response object from the fetched data and save it to disk in a pre-defined cache directory.

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Application Behavior

Develop a web application using aiohttp server:

• Implement a single route handler to retrieve exchange rate data.
• Support queries both with and without a date.
• If no date is provided, use today’s date.
• Use the API wrapper to get data:
  • If the data is cached — use the cached result.
  • If it’s a new request — fetch, format, and save to cache before responding.

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Error Handling

• If an unknown currency is provided — return HTTP 404.
• If an invalid date is provided — return HTTP 422.

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Type Hints

• Add type annotations throughout the codebase.
• Ensure the application passes mypy checks in strict mode.

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📦 Dependencies used in my project

Core Dependencies (dependencies)

• aiohttp – asynchronous HTTP server and client
• aiofiles – async file I/O
• msgspec – fast data validation and serialization
• python-dotenv – load environment variables from .env files
• redis – Redis client for Python

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🛠 Developer Tools

Group dev

• aioresponses – mock HTTP responses for aiohttp
• coverage – code coverage reports
• fakeredis – in-memory fake Redis server for testing

Group lint

• mypy – static type checker
• ruff – fast Python linter & formatter
• types-aiofiles – type stubs for aiofiles

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🧪 In addition to the assignment, I

• ✅ Wrote unit tests using Python's standard unittest module
• ✅ Added optional Redis-based caching alongside disk caching

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🚀 Running the Application

Clone repository:

git clone https://github.com/bizoxe/exchange-rate-web-app.git

Start Valkey using Docker

docker compose up -d

Run the Application

uv run webapp

Once you launch the app, navigate:

• get exchange rates for a currency (latest): http://localhost:8080/rates/usd
• get exchange rates for a currency on a specific date: http://localhost:8080/rates/usd/2025-01-01

Note:

You can use file-based caching instead of Redis. In this case, you don’t need to run Docker.

Use the following command to switch to file caching:

export STORAGE_TYPE=file

Then simply run the application with:

uv run webapp