The Same Request, Now from Code

In APIs for Beginners, requests to web services were typed by hand with curl. Here the same kind of request is sent by a program, and the answer arrives as the lists and dictionaries of Chapter 6, ready to use. The example is a question with a real, changing answer: at today's exchange rate, what was the €86.40 spent on a trip abroad worth in dollars?

It is the same phone call as in that book. The difference is that now the program dials the number, listens to the answer, and writes it down for you.

One-Line Recap

A web service that programs talk to is an API. A program sends it a GET request for an address, a URL, optionally with query parameters after a question mark that say exactly what it wants. The service replies with a status code, where 200 means success, and a body, usually JSON. If any of that is new, APIs for Beginners explains each part properly; this page only needs the one-line version.

requests.get

The requests package installed in Chapter 9 sends the request. requests.get takes the URL, and the query parameters as a dictionary passed as params, so requests builds the question-mark part correctly for you. The timeout argument says how many seconds to wait at most; the next topic explains why it must always be there. The service used here publishes daily reference exchange rates and needs no key. Its address and answer format are as of 2026, and the page on it at frankfurter.dev is the place to check if anything below stops matching.

from decimal import Decimal

import requests

response = requests.get(
    "https://api.frankfurter.dev/v2/rates",
    params={"base": "EUR", "quotes": "USD"},
    timeout=5,
)
print("Status:", response.status_code)
data = response.json()
print(data)

rate = Decimal(str(data[0]["rate"]))
spent = Decimal("86.40")
print(f"EUR {spent} was USD {spent * rate:.2f} at the rate of {data[0]['date']}")

Status: 200
[{'date': '2026-09-23', 'base': 'EUR', 'quote': 'USD', 'rate': 1.1452}]
EUR 86.40 was USD 98.95 at the rate of 2026-09-23

Reading the Response

response.status_code is the status code: 200, success. response.json() reads the JSON body and gives back Python data, already parsed. For this service it is a list containing one dictionary per currency asked for, with the date, the base currency, the quoted currency and the rate. Reading the rate is Chapter 6's skill: the first item of the list, then its rate key, data[0]["rate"].

The Conversion

The rate arrives as a float, because JSON numbers become floats. Money in this book is Decimal, so the program turns the rate into text with str and then into a Decimal, which keeps exactly the digits the service sent. Multiplying the amount by the rate gives the dollar value, formatted to two places only when printed.

The Part That May Change

Everything on this page about Python, requests.get, params, status_code and json(), works the same with any web service. The address, the parameter names and the shape of the answer belong to this one service, and services change them from time to time. If the service changes, the code needs a new URL and a new line to find the rate in the answer; nothing else.