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refactor(book-app): add type annotations and input validation #82

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DanWahlin wants to merge 1 commit into from
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refactor(book-app): add type annotations and input validation #82

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22 changes: 15 additions & 7 deletions samples/book-app-project/book_app.py
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Original file line number Diff line number Diff line change
Expand Up @@ -6,7 +6,7 @@
collection = BookCollection()


def show_books(books):
def show_books(books: list) -> None:
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Copilot AI Apr 16, 2026

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show_books is annotated as books: list, which is effectively list[Any] and doesn’t convey the expected element type. Since this function assumes book has .read/.title/.author/.year, the annotation should be parameterized (e.g., list[Book] / List[Book]) or widened to a read-only abstraction like Sequence[Book] for better type safety and to match the project’s use of typed BookCollection return values.

See below for a potential fix:

from typing import Protocol, Sequence
from books import BookCollection


class SupportsShownBook(Protocol):
    read: bool
    title: str
    author: str
    year: int


# Global collection instance
collection = BookCollection()


def show_books(books: Sequence[SupportsShownBook]) -> None:

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"""Display books in a user-friendly format."""
if not books:
print("No books found.")
Expand All @@ -21,16 +21,24 @@ def show_books(books):
print()


def handle_list():
def handle_list() -> None:
books = collection.list_books()
show_books(books)


def handle_add():
def handle_add() -> None:
print("\nAdd a New Book\n")

title = input("Title: ").strip()
if not title:
print("\nError: Title cannot be empty.\n")
return

author = input("Author: ").strip()
if not author:
print("\nError: Author cannot be empty.\n")
return

year_str = input("Year: ").strip()

try:
Expand All @@ -41,7 +49,7 @@ def handle_add():
print(f"\nError: {e}\n")


def handle_remove():
def handle_remove() -> None:
print("\nRemove a Book\n")

title = input("Enter the title of the book to remove: ").strip()
Expand All @@ -50,7 +58,7 @@ def handle_remove():
print("\nBook removed if it existed.\n")


def handle_find():
def handle_find() -> None:
print("\nFind Books by Author\n")

author = input("Author name: ").strip()
Expand All @@ -59,7 +67,7 @@ def handle_find():
show_books(books)


def show_help():
def show_help() -> None:
print("""
Book Collection Helper

Expand All @@ -72,7 +80,7 @@ def show_help():
""")


def main():
def main() -> None:
if len(sys.argv) < 2:
show_help()
return
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