Library Management System (Python OOP)

A fully object-oriented Library Management System built in Python, demonstrating class design, inheritance, custom exceptions, and JSON persistence. Tracks books, members (basic/premium), borrowing, returning, overdue fines, and reporting through a command-line interface. Built as the OOP task for the Enischyo Interns Python Development internship program.

Keywords: python oop project, library management system, inheritance, custom exception class, JSON persistence, CLI application, unittest, internship project, python class design.

Quick start

git clone https://github.com/maida-maryam06/library-management-system.git
cd library-management-system
python main.py

No external dependencies — pure Python standard library (json, os, datetime, unittest).

Features

• Full OOP class design, each with complete docstrings:
  • Book — title, author, ISBN, genre, copy counts, published year
  • Member — basic membership (max 2 borrowed books at once)
  • PremiumMember(Member) — inherits from Member, raises the borrow limit to 5 and overrides validate_borrow() accordingly
  • Librarian — staff member with employee ID and shift
  • Transaction — one borrow/return record with due date and fine
  • Library — the central orchestrator owning all books, members, and transactions
• Custom exception hierarchy rooted at LibraryError, used for every error case (book/member not found, no copies available, borrow limit exceeded, duplicate ISBN/member ID, returning a book never borrowed).
• Core Library methods:
  • add_book() / remove_book() — catalog management, with removal blocked while copies are out on loan
  • search_books(query) — matches title OR author OR genre, case-insensitively
  • borrow_book(member_id, isbn) — validates availability and borrow limit, decrements copies_available, appends to the member's borrowed_books, creates a Transaction
  • return_book(member_id, isbn) — closes the transaction, charges Rs. 10/day fine for every day past the 14-day loan period
  • get_overdue_books() — all transactions still out and past due
  • generate_report() — formatted summary (catalog size, membership breakdown, overdue list with running fines)
• JSON persistence: on startup, Library loads library_data.json (if present) and reconstructs live objects — including correctly rebuilding PremiumMember instances (not generic Member) so the 5-book limit survives a restart.
• Interactive CLI menu with try/except LibraryError handling around every operation.
• 10 unit tests (unittest) covering every major method, the inheritance/override behavior, the custom exceptions, and the JSON round-trip.

Project structure

library-management-system/
├── book.py             # Book class
├── member.py           # Member base class + PremiumMember subclass
├── librarian.py        # Librarian class
├── transaction.py      # Transaction class (borrow/return/fine logic)
├── exceptions.py        # LibraryError and subclasses
├── library.py           # Library orchestrator (all core methods + JSON persistence)
├── main.py              # CLI menu application
├── test_library.py       # unittest suite (10 tests)
└── README.md

library_data.json is created automatically the first time you run main.py and add a book or member — it is not committed empty, since the app generates it on first use.

Borrowing rules

Membership	Max books borrowed at once
Basic	2
Premium	5

• Loan period: 14 days from the borrow date.
• Late fine: Rs. 10 per day for every day past the due date (no fine for on-time or early returns).

Running the app

python3 main.py

========================================
   LIBRARY MANAGEMENT SYSTEM
========================================
1. Add a book
2. Remove a book
3. Search books (title/author/genre)
4. Register a member
5. Borrow a book
6. Return a book
7. View overdue books
8. Generate library report
9. List all books
10. List all members
11. Exit
========================================

Every action saves immediately to library_data.json, so you can quit and resume later without losing data.

Running the tests

python -m unittest test_library.py -v

The test suite uses a separate test_library_data.json file (created and deleted automatically in setUp/tearDown), so running the tests never touches your real library_data.json.

Actual test output

The following is the real output from running the test suite in this repo (10 tests, all passing):

test_01_add_book (test_library.TestLibraryManagementSystem.test_01_add_book) ... ok
test_02_remove_book (test_library.TestLibraryManagementSystem.test_02_remove_book) ... ok
test_03_search_books (test_library.TestLibraryManagementSystem.test_03_search_books) ... ok
test_04_borrow_book_success (test_library.TestLibraryManagementSystem.test_04_borrow_book_success) ... ok
test_05_borrow_book_no_copies_available (test_library.TestLibraryManagementSystem.test_05_borrow_book_no_copies_available) ... ok
test_06_borrow_limit_basic_vs_premium (test_library.TestLibraryManagementSystem.test_06_borrow_limit_basic_vs_premium) ... ok
test_07_return_book_on_time_and_overdue_fine (test_library.TestLibraryManagementSystem.test_07_return_book_on_time_and_overdue_fine) ... ok
test_08_get_overdue_books (test_library.TestLibraryManagementSystem.test_08_get_overdue_books) ... ok
test_09_persistence_save_and_load (test_library.TestLibraryManagementSystem.test_09_persistence_save_and_load) ... ok
test_10_generate_report_and_librarian (test_library.TestLibraryManagementSystem.test_10_generate_report_and_librarian) ... ==================================================

LIBRARY REPORT: Test Library
==================================================
Address: 1 Test St
--------------------------------------------------
Total titles in catalog: 3
Total copies owned:      4
Copies available now:    4
--------------------------------------------------
Total members:           2
  Basic members:         1
  Premium members:       1
--------------------------------------------------
Total transactions:      0
Currently borrowed:      0
Currently overdue:       0
==================================================
ok

----------------------------------------------------------------------
Ran 10 tests in 0.106s

OK

Design notes

• Why a separate Transaction class? borrow_book() is required to "create a Transaction record," so transactions are modeled as first-class objects with their own borrow/due/return dates and fine calculation, rather than as loose fields bolted onto Member or Book.
• Why does PremiumMember override validate_borrow() instead of just changing BORROW_LIMIT? Both are actually done together: BORROW_LIMIT is a class attribute that PremiumMember overrides to 5, and validate_borrow() is overridden too so the error message correctly says "Premium member" vs the basic message — Library.borrow_book() calls member.validate_borrow() polymorphically without needing to know which subclass it's dealing with.
• Why block remove_book() while copies are on loan? Removing a book that members currently have borrowed would leave their borrowed_books lists and open Transaction records pointing at a title that no longer exists in the catalog — an inconsistent state the system actively prevents.
• Why is Librarian not a subclass of Member? A librarian doesn't borrow books and has a different attribute set (employee_id, shift) — modeling them as siblings rather than parent/child avoids inheriting irrelevant fields and methods.

License

MIT — free to use, copy, and modify.