Wrapping an API in a class

One place that knows about the API

Scattering requests.get calls through a codebase means the base URL, the token and the error handling are scattered too. A client class puts them in one place:

class WeatherClient:
    def __init__(self, base_url, token=None):
        self.base_url = base_url
        self.token = token

    def _headers(self):
        if self.token:
            return {"Authorization": "Bearer " + self.token}
        return {}

    def get_weather(self, city):
        r = requests.get(
            self.base_url + "/weather",
            params={"city": city},
            headers=self._headers(),
        )
        r.raise_for_status()
        return r.json()

Now changing the base URL, adding a header or adding retries is one edit. The methods speak the language of the problem — get_weather("London") — rather than the language of HTTP.

Your turn: build WeatherClient with get_weather(city) returning the parsed body, and get_temperature(city) returning just the number or None for an unknown city.

Why this whole course used a stub

Every lesson here talked to a scripted service rather than the internet, and that was not a limitation of the browser — it is how you should test an API client anywhere.

A test that makes real network calls is slow, needs credentials, fails when someone else's server is down, and cannot reproduce a 500 on demand. A fake makes every one of those cases instant and deterministic.

The technique is to inject the thing that talks to the network, rather than reaching for it directly:

class Client:
    def __init__(self, http):     # <- passed in, not imported
        self.http = http

    def temperature(self, city):
        return self.http.get("/weather", params={"city": city}).json()["temp_c"]

Now a test passes a stub with a scripted answer, and production passes the real thing. This is dependency injection, and it is the difference between a client you can test and one you can only hope about.

Your turn: write Client taking an http object, with temperature(city) returning the number and is_warm(city) returning True above 20. Then write FakeHttp — a stub with a scripted table — so the class can be tested with no network at all.