Exercises — Module 01: Introduction to APIs¶

Work through exercises in order — they're designed to build on each other. Attempt each problem genuinely before looking at the solution. Seeing the solution first might feel like progress, but it isn't.

Instructions¶

1. Attempt first. Spend at least the estimated time on each problem before checking hints or solutions.
2. Write your work. Don't just run code mentally — actually type and run your attempt.
3. Check your answer against the acceptance criteria, not just the solution code.
4. Score yourself honestly in the Scoring Log at the bottom.
5. If you're stuck after a genuine effort, use the hints one at a time — not all at once.

Difficulty Legend¶

Exercise 1: Annotate an HTTP Transaction [🟢 Easy] [1 pt]¶

Context¶

Understanding the anatomy of HTTP requests and responses is fundamental — every API interaction is an HTTP transaction. This exercise confirms you can read and interpret one.

Task¶

Below is a raw HTTP exchange. Annotate each line with what it represents — identify the method, URL, headers, status code, and body sections.

POST /api/v1/users HTTP/1.1
Host: api.example.com
Content-Type: application/json
Authorization: Bearer eyJhbGciOiJSUzI1NiJ9...
Content-Length: 67

{"name": "Bob Smith", "email": "bob@example.com", "role": "editor"}

---

HTTP/1.1 201 Created
Content-Type: application/json
Location: /api/v1/users/99
Date: Mon, 09 Jun 2026 10:00:00 GMT

{"id": 99, "name": "Bob Smith", "email": "bob@example.com", "role": "editor"}

Write your annotation in comments or in a separate document. For each line, state: 1. What part of the request/response is it? 2. What does its value mean in this specific context?

Requirements¶

• Identify all 4 parts of the request (method, URL+protocol, headers, body)
• Identify what Authorization: Bearer ... is for
• Explain the meaning of 201 Created
• Explain what the Location header tells the client

Hints¶

Expected Output / Acceptance Criteria¶

Your annotation correctly identifies: - POST as the HTTP method meaning "create a new resource" - /api/v1/users as the resource being acted upon - Content-Type: application/json as declaring the body format - Authorization: Bearer ... as carrying authentication credentials - 201 Created as the success code for resource creation - Location: /api/v1/users/99 as pointing to the newly created resource

Solution¶

# REQUEST
POST /api/v1/users HTTP/1.1
# ↑ Method: POST = create a new resource
# ↑ Resource: /api/v1/users = the users collection
# ↑ Protocol: HTTP/1.1

Host: api.example.com
# ↑ Required header: tells the server which virtual host to serve

Content-Type: application/json
# ↑ Declares the body format — the server must parse it as JSON

Authorization: Bearer eyJhbGciOiJSUzI1NiJ9...
# ↑ Authentication credentials — a JWT Bearer token

Content-Length: 67
# ↑ Size of the request body in bytes

                              ← blank line separates headers from body
{"name": "Bob Smith", "email": "bob@example.com", "role": "editor"}
# ↑ Request body: the data to create the new user

# RESPONSE
HTTP/1.1 201 Created
# ↑ Status code 201 = a new resource was successfully created

Content-Type: application/json
# ↑ Response body is JSON

Location: /api/v1/users/99
# ↑ Points to the URL of the newly created resource
# ↑ The client can navigate to this URL to read the resource

{"id": 99, "name": "Bob Smith", "email": "bob@example.com", "role": "editor"}
# ↑ The created resource, including the server-assigned ID

Exercise 2: Identify REST Constraint Violations [🟢 Easy] [1 pt]¶

Context¶

An API that violates REST constraints isn't necessarily bad — but understanding which constraints it violates and why helps you reason about the tradeoffs.

Task¶

For each API design below, identify which REST constraint(s) it violates and why.

API Design A:

POST /api/do-action
Body: {"action": "get_user", "userId": 42}

API Design B:

GET /api/users?session_id=abc123

API Design C:

GET /api/users/42
Response: HTTP 200 OK
Body: {"success": false, "error": "User not found"}

Requirements¶

• Identify at least one violated constraint for each design
• Explain why each is a violation

Hints¶

Expected Output / Acceptance Criteria¶

Correct identification of at least one violation per design, with accurate reasoning.

Solution¶

Exercise 3: Make Real API Calls with Python [🟡 Medium] [2 pts]¶

Context¶

Translating concepts to working code is how they become durable skills. This exercise has you make several API calls, handle different response codes, and work with the data — applying the HTTP anatomy from the module.

Task¶

Write a Python script that does the following, using the JSONPlaceholder API:

1. Fetch the first 5 posts (GET /posts?_limit=5)
2. For each post, print: the post title and the user ID (from the userId field)
3. Fetch the user for the first post only (GET /users/{userId})
4. Print the user's name and company name (user['company']['name'])
5. Handle the case where a resource returns 404 (simulate with /users/99999)

Requirements¶

• Uses Python requests library
• Correctly uses response.json() to parse responses
• Handles 404 separately from other errors (not just raise_for_status() for everything)
• All print output is labelled (not just raw values)
• Code has at least one comment explaining non-obvious parts

Hints¶

Expected Output / Acceptance Criteria¶

=== First 5 Posts ===
1. "sunt aut facere..." (user: 1)
2. "qui est esse" (user: 1)
3. "ea molestias quasi..." (user: 1)
4. "eum et est occaecati" (user: 1)
5. "nesciunt quas odio" (user: 1)

=== Author of Post 1 ===
Name: Leanne Graham
Company: Romaguera-Crona

=== Testing 404 Handling ===
User 99999 not found (404)

Solution¶

import requests

BASE_URL = "https://jsonplaceholder.typicode.com"

def fetch_user(user_id: int) -> dict | None:
    """Fetch a user by ID. Returns None if not found (404)."""
    response = requests.get(f"{BASE_URL}/users/{user_id}")
    if response.status_code == 404:
        return None
    response.raise_for_status()    # Raise for 5xx, 429, etc.
    return response.json()

# Step 1 & 2: Fetch first 5 posts
response = requests.get(f"{BASE_URL}/posts", params={"_limit": 5})
response.raise_for_status()
posts = response.json()

print("=== First 5 Posts ===")
for post in posts:
    # Truncate long titles for readable output
    title_preview = post['title'][:40] + "..." if len(post['title']) > 40 else post['title']
    print(f"{post['id']}. \"{title_preview}\" (user: {post['userId']})")

# Step 3 & 4: Fetch author of first post
first_post = posts[0]
print(f"\n=== Author of Post {first_post['id']} ===")
author = fetch_user(first_post['userId'])
if author:
    print(f"Name: {author['name']}")
    print(f"Company: {author['company']['name']}")

# Step 5: Test 404 handling
print("\n=== Testing 404 Handling ===")
missing = fetch_user(99999)
if missing is None:
    print("User 99999 not found (404)")

Exercise 4: Compare REST and GraphQL Data Fetching [🟡 Medium] [2 pts]¶

Context¶

The theory section explained over-fetching and under-fetching conceptually. This exercise makes the comparison concrete by asking you to design both the REST and GraphQL approaches for a given view.

Task¶

You're building a "team dashboard" that shows each team member's name, their current project name, and how many tasks are assigned to them.

The REST API has three endpoints: - GET /team-members → list of { id, name, project_id } - GET /projects/{id} → { id, name, description, deadline } - GET /team-members/{id}/tasks/count → { count: N }

Part A: Write pseudocode (or actual code) showing the REST calls needed to build the dashboard for 5 team members. Count the total number of HTTP requests.

Part B: Write the equivalent GraphQL query that fetches all needed data in one request. (Assume the GraphQL API has the types and fields you need.)

Part C: Write 2–3 sentences explaining the trade-off between the two approaches for this use case.

Requirements¶

• Part A identifies the correct number of REST requests
• Part B is valid GraphQL query syntax
• Part C identifies at least one advantage and one disadvantage of each approach

Hints¶

Expected Output / Acceptance Criteria¶

• Part A: 11 total REST requests (1 + 5 projects + 5 task counts)
• Part B: A valid GraphQL query fetching name, project.name, and taskCount in one request
• Part C: Honest assessment of the tradeoffs

Solution¶

# Request 1: get all team members
members = GET /team-members
# → [{ id: 1, name: "Alice", project_id: 10 }, { id: 2, ... }, ...]

for member in members:
    # Request N: get each member's project (5 requests for 5 members)
    project = GET /projects/{member['project_id']}

    # Request N: get each member's task count (5 more requests)
    tasks = GET /team-members/{member['id']}/tasks/count

# Total: 1 + 5 + 5 = 11 HTTP requests to render the dashboard

query TeamDashboard {
  teamMembers {
    name
    project {
      name
    }
    taskCount
  }
}
# Total: 1 HTTP request, 1 GraphQL query

Exercise 5: Debug a Broken API Client [🔴 Hard] [3 pts]¶

Context¶

This multi-step exercise requires you to identify multiple problems in a real-ish API client and fix them. The bugs are representative of common beginner mistakes.

Task¶

The following Python script is supposed to fetch the top 3 posts and create a new comment on the first one, but it has multiple bugs. Find and fix all of them.

import requests
import json

# Bug-hunting exercise: this code has multiple problems
# Find all of them, explain why each is a bug, and provide the fix

BASE = "https://jsonplaceholder.typicode.com"

# Fetch posts
posts_response = requests.get(BASE + "/posts?limit=3")
posts = posts_response.text()           # BUG 1

# Get first post
first_post = posts[0]
post_id = first_post.id                 # BUG 2

# Create a comment on the post
comment_data = json.dumps({
    "postId": post_id,
    "name": "Great post!",
    "email": "reader@example.com",
    "body": "Really enjoyed reading this."
})

comment_response = requests.post(
    BASE + f"/posts/{post_id}/comments",
    data=comment_data                   # BUG 3 (partial — works but is wrong idiomatically)
)

if comment_response == 201:             # BUG 4
    print("Comment created!")
    print(comment_response.json['id'])  # BUG 5
else:
    print(f"Failed: {comment_response.status_code}")

Requirements¶

• Identifies all 5 bugs
• Explains why each is a bug (not just what the fix is)
• Provides correct fixed code that runs without errors
• Fixed code prints "Comment created!" and the comment's assigned ID

Hints¶

Expected Output / Acceptance Criteria¶

Fixed code should output:

Comment created!
Comment ID: 501

Solution¶

import requests

BASE = "https://jsonplaceholder.typicode.com"

# --- FIX 1: Use .json() method (not .text()) to parse the JSON response ---
# .text is a property that returns the raw string
# .json() is a method that parses the string to a Python dict/list
posts_response = requests.get(BASE + "/posts", params={"_limit": 3})
posts = posts_response.json()           # ← was: posts_response.text()

# --- FIX 2: Use dict bracket syntax, not attribute access ---
# Python dicts are accessed with [] not .property
first_post = posts[0]
post_id = first_post['id']              # ← was: first_post.id

# --- FIX 3: Pass the raw dict to json= and let requests serialise it ---
# Using data= with a pre-serialised string doesn't set Content-Type: application/json
# Using json= with a dict: requests serialises it AND sets the correct Content-Type header
comment_response = requests.post(
    BASE + f"/posts/{post_id}/comments",
    json={                              # ← was: data=json.dumps({...})
        "postId": post_id,
        "name": "Great post!",
        "email": "reader@example.com",
        "body": "Really enjoyed reading this."
    }
)

# --- FIX 4: Compare status_code (int), not the Response object itself ---
# comment_response is a requests.Response object, not an integer
# Comparing a Response to 201 is always False
if comment_response.status_code == 201:    # ← was: comment_response == 201
    print("Comment created!")

    # --- FIX 5: json() is a method, not a property — call it with () ---
    comment = comment_response.json()       # ← was: comment_response.json['id']
    print(f"Comment ID: {comment['id']}")
else:
    print(f"Failed: {comment_response.status_code}")

Scoring Log¶

Record your performance honestly. Include the date and whether you used hints.

Passing threshold: 6/9 (67%). Aim for 8/9 (89%) before taking the test.