Exercise: Comprehensions, Exceptions, and Dataclasses

Part 1: For Loops Into Comprehensions

Rewrite each for loop below as a list comprehension.

Build a list of slugs from project names:

Python

project_names = ["Payments API", "Developer Portal", "Ops Console"]

slugs = []
for name in project_names:
    slugs.append(name.lower().replace(" ", "-"))

Build a list of titles for tasks that aren't done:

Python

tasks = [
    {"title": "ship docs", "done": False},
    {"title": "cut release", "done": True},
    {"title": "announce launch", "done": False},
]

open_titles = []
for task in tasks:
    if not task["done"]:
        open_titles.append(task["title"])

Part 2: Raise and Catch an Exception

Write validate_project_name(name) that strips the input and raises ValueError("Project name cannot be blank.") if the result is empty. Otherwise it returns the cleaned name.

Then call it with " " inside a try/except block and print the caught exception's message.

Part 3: A Simple Dataclass

Define a Project dataclass with three fields:

• name: str
• slug: str
• archived: bool = False

Create a Project instance, print it, and confirm archived defaults to False.

Solution

Python

from dataclasses import dataclass


project_names = ["Payments API", "Developer Portal", "Ops Console"]

slugs = [name.lower().replace(" ", "-") for name in project_names]


tasks = [
    {"title": "ship docs", "done": False},
    {"title": "cut release", "done": True},
    {"title": "announce launch", "done": False},
]

open_titles = [task["title"] for task in tasks if not task["done"]]


def validate_project_name(name: str) -> str:
    cleaned = name.strip()
    if not cleaned:
        raise ValueError("Project name cannot be blank.")
    return cleaned


@dataclass
class Project:
    name: str
    slug: str
    archived: bool = False


if __name__ == "__main__":
    print(slugs)
    print(open_titles)

    try:
        validate_project_name("  ")
    except ValueError as e:
        print(f"Validation failed: {e}")

    payments = Project(name="Payments API", slug="payments-api")
    print(payments)
    print(payments.archived)

Success

If the script prints the two comprehension results, the ValueError message, the Project repr, and False for archived, you've practiced enough of the chapter's tools to move on.