Building a Currency Converter in Python (with Real-Time Exchange Rates)

Currency conversion is a common utility in global applications such as travel apps, financial tools, and e-commerce systems. In this article, we’ll learn how to build a functional Currency Converter in Python using real-time exchange rates from a public API.

This script will allow users to:

• Input an amount

• Choose a source and target currency

• Get the latest exchange rate

• See the converted value instantly

We’ll use the ExchangeRate-API (free tier) or exchangerate.host which is completely free and doesn't require an API key.

Step 1: Install Required Libraries

We’ll use the built-in json module and the third-party requests library to make HTTP calls. If you don’t have requests, install it with:

pip install requests

Step 2: Import Necessary Modules

Start by importing the required modules.

import requests

The requests module is used to make HTTP requests to the currency exchange API and fetch JSON data.

Step 3: Define the Currency Conversion Function

We'll write a function that accepts the base currency, target currency, and amount to convert.

def convert_currency(base_currency, target_currency, amount):
    url = f"https://api.exchangerate.host/latest?base={base_currency.upper()}&symbols={target_currency.upper()}"

    try:
        response = requests.get(url)
        data = response.json()

        if target_currency.upper() in data['rates']:
            rate = data['rates'][target_currency.upper()]
            converted_amount = amount * rate
            return converted_amount, rate
        else:
            print("Currency code not found.")
            return None, None

    except Exception as e:
        print(f"An error occurred: {e}")
        return None, None

Explanation

• The API returns real-time exchange rates in JSON format.

• We extract the specific rate for the target currency.

• Multiply the rate by the amount to get the converted value.

• The function also handles possible errors, such as invalid currency codes or network issues.

Step 4: Get User Input and Perform Conversion

Let’s now build a simple interface to let the user enter the base currency, target currency, and the amount to convert.

if __name__ == "__main__":
    print("Welcome to the Currency Converter")

    base = input("Enter base currency (e.g., USD): ").strip()
    target = input("Enter target currency (e.g., EUR): ").strip()
    try:
        amount = float(input("Enter amount to convert: "))
    except ValueError:
        print("Invalid amount.")
        exit()

    result, rate = convert_currency(base, target, amount)

    if result is not None:
        print(f"\nExchange Rate: 1 {base.upper()} = {rate:.4f} {target.upper()}")
        print(f"Converted Amount: {amount} {base.upper()} = {result:.2f} {target.upper()}")

What This Does

• Prompts the user to enter currencies and the amount.

• Converts the amount using the convert_currency() function.

• Displays the exchange rate and the result.

Sample Output

Welcome to the Currency Converter
Enter base currency (e.g., USD): usd
Enter target currency (e.g., EUR): eur
Enter amount to convert: 100

Exchange Rate: 1 USD = 0.9132 EUR
Converted Amount: 100 USD = 91.32 EUR

Why Use exchangerate.host?

• It’s free and doesn’t require an API key

• Simple and fast JSON responses

• Offers historical rates, conversion, and time series if needed

You can also replace it with another API like ExchangeRate-API, OpenExchangeRates, or Fixer.io if you want more advanced features or authenticated requests.

Additional Features You Can Add

1. GUI Interface: Use tkinter to create a desktop GUI.

2. Dropdown Menus: Load available currency codes dynamically.

3. Historical Conversion: Add date selection to convert with historical rates.

4. Command-Line Arguments: Support script usage from the terminal with arguments.

Conclusion

You now have a working real-time currency converter in Python. This script demonstrates how to integrate external APIs with Python logic to create practical and user-friendly tools. With a bit of extension, you can turn this into a desktop app or even integrate it into a web service.