Module 14: urllib error handling for fetch_post — and why not requests?

[dab00gieman]

python-study-Neo_1/curriculum/14_apis_requests/exercises.py:

import urllib.request
import json
URL = "https://jsonplaceholder.typicode.com/posts/1"

# TODO: Write a function named 'fetch_post' that makes a GET request to the URL using urllib.
# The function should return the dictionary loaded from the JSON response.
# Handle potential errors and return None if the request fails.

For the "handle potential errors" part, which failures should the canonical solution catch — urllib.error.URLError, HTTPError, plus json.JSONDecodeError for a malformed body? And since the module is literally named "APIs & Requests" but uses urllib, is the stdlib-first choice (per the README: "Everything runs on the standard library only unless a module says otherwise") the reason, with requests as a later optional upgrade?

[mgkvibez]

Here's a complete, correct fetch_post for that scaffold:

import urllib.request
import urllib.error
import json

def fetch_post():
    try:
        with urllib.request.urlopen(URL) as response:
            if response.status != 200:
                return None
            return json.load(response)
    except (urllib.error.URLError, json.JSONDecodeError):
        return None

Three details that make this the "exam answer" version:

• import urllib.error is not optional. import urllib.request does not guarantee the urllib.error name is bound — the subtlety has bitten everyone once. HTTPError (404s etc.) subclasses URLError, so the one tuple catches connection failures and HTTP errors.
• json.load(response) reads the response body stream directly — no response.read().decode() + json.loads() middle step needed.
• The explicit status != 200 check is belt-and-braces (urlopen raises for most non-2xx anyway) but makes the "API returned something weird → None" contract obvious.

Why urllib and not requests: the module is stdlib-only by design — the curriculum teaches the standard library first so there's zero install friction and you see what "just making an HTTP request" actually involves. The module name (14_apis_requests) hints the intended follow-up: solve it again with requests and diff the two. The whole function becomes:

import requests

def fetch_post():
    try:
        r = requests.get(URL, timeout=10)
        r.raise_for_status()
        return r.json()
    except requests.RequestException:
        return None

— which is exactly the readability lesson the comparison is meant to land.