Library Management System

easy · CRUD + business rules

Brief-reported interview attribution (unverified): Amazon, Microsoft

Design a library. It tracks books (copies available), members, and loans. A member may borrow at most 3 books at a time, and may not borrow the same book twice. A loan lasts 14 days; returning late costs $1 per day over 14.

class Library:
    def __init__(self):
    def add_book(self, book_id, title, author, copies):
        # adding the same book_id again increases total and available copies
    def register_member(self, member_id, name):
        # registering the same member_id again is a no-op
    def borrow(self, member_id, book_id):
        # -> True if the loan is made, False otherwise
    def return_book(self, member_id, book_id, days_borrowed):
        # -> fine in dollars (int), or None if the member never borrowed that book
    def available_copies(self, book_id):
        # -> int (0 for an unknown book)
    def borrowed_books(self, member_id):
        # -> sorted list of book_ids the member currently has (empty for unknown member)
    def search_by_title(self, query):
        # -> sorted list of book_ids whose title contains the query (case-insensitive)

Rules. borrow returns False when the member or book is unknown, no copy is available, the member already has 3 books, or the member already has this book. return_book returns max(0, days_borrowed - 14) * 1.

Money units: late fees are whole dollars, not cents; six days late returns 6.

Tests use explicit inputs and injected clocks/callbacks. No network, real threads or application-server execution is involved.

Public demo

# Public demo: run after implementing the class API above.
l = Library()
for bid, title, copies in [('B1', 'Python Crash Course', 1), ('B2', 'Fluent Python', 2), ('B3', 'Clean Code', 1), ('B4', 'Design Patterns', 1)]:
    l.add_book(bid, title, 'Author', copies)
l.register_member('M1', 'Asha')
l.register_member('M2', 'Ravi')
print(l.borrow('M1', 'B1'))
print(l.available_copies('B1'))

Starter code

class Library:

    def __init__(self):
        """Initialize the state described in the problem."""
        pass

    def add_book(self, book_id, title, author, copies):
        """adding the same book_id again increases total and available copies"""
        pass

    def register_member(self, member_id, name):
        """registering the same member_id again is a no-op"""
        pass

    def borrow(self, member_id, book_id):
        """-> True if the loan is made, False otherwise"""
        pass

    def return_book(self, member_id, book_id, days_borrowed):
        """-> fine in dollars (int), or None if the member never borrowed that book"""
        pass

    def available_copies(self, book_id):
        """-> int (0 for an unknown book)"""
        pass

    def borrowed_books(self, member_id):
        """-> sorted list of book_ids the member currently has (empty for unknown member)"""
        pass

    def search_by_title(self, query):
        """-> sorted list of book_ids whose title contains the query (case-insensitive)"""
        pass

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