From c2c51fc5d6b7abd493bceafe98b0472cb5221419 Mon Sep 17 00:00:00 2001
From: nickzerjeski <nick@zerjeski.de>
Date: Mon, 13 Apr 2026 10:44:32 +0200
Subject: [PATCH 1/4] feat(other): add basic BankAccount OOP class

---
 other/bank_account.py | 60 +++++++++++++++++++++++++++++++++++++++++++
 1 file changed, 60 insertions(+)
 create mode 100644 other/bank_account.py

diff --git a/other/bank_account.py b/other/bank_account.py
new file mode 100644
index 000000000000..c3aa5a07b1ef
--- /dev/null
+++ b/other/bank_account.py
@@ -0,0 +1,60 @@
+"""
+Simple BankAccount class demonstrating core OOP concepts.
+"""
+
+
+class BankAccount:
+    """
+    Basic bank account model with encapsulated account number and balance.
+
+    >>> account = BankAccount("ACC-1001", initial_balance=100.0)
+    >>> account.balance
+    100.0
+    >>> account.deposit(50)
+    150.0
+    >>> account.withdraw(20)
+    130.0
+    >>> account.account_number
+    'ACC-1001'
+    """
+
+    def __init__(self, account_number: str, initial_balance: float = 0.0) -> None:
+        if not account_number:
+            raise ValueError("account_number must be provided")
+        if initial_balance < 0:
+            raise ValueError("initial_balance cannot be negative")
+
+        self.__account_number = account_number
+        self._balance = float(initial_balance)
+
+    @property
+    def account_number(self) -> str:
+        """Read-only public accessor for the encapsulated account number."""
+        return self.__account_number
+
+    @property
+    def balance(self) -> float:
+        """Current account balance."""
+        return self._balance
+
+    def deposit(self, amount: float) -> float:
+        """Deposit a positive amount and return updated balance."""
+        if amount <= 0:
+            raise ValueError("deposit amount must be positive")
+        self._balance += amount
+        return self._balance
+
+    def withdraw(self, amount: float) -> float:
+        """Withdraw a positive amount and return updated balance."""
+        if amount <= 0:
+            raise ValueError("withdraw amount must be positive")
+        if amount > self._balance:
+            raise ValueError("insufficient funds")
+        self._balance -= amount
+        return self._balance
+
+
+if __name__ == "__main__":
+    import doctest
+
+    doctest.testmod()

From 1661ee00f5cab450583f1a9b9651f771d7145b44 Mon Sep 17 00:00:00 2001
From: Nick Zerjeski <57059725+nickzerjeski@users.noreply.github.com>
Date: Tue, 14 Apr 2026 10:18:12 +0200
Subject: [PATCH 2/4] Update other/bank_account.py

Co-authored-by: Copilot <175728472+Copilot@users.noreply.github.com>
---
 other/bank_account.py | 3 +++
 1 file changed, 3 insertions(+)

diff --git a/other/bank_account.py b/other/bank_account.py
index c3aa5a07b1ef..6ada347d6240 100644
--- a/other/bank_account.py
+++ b/other/bank_account.py
@@ -1,5 +1,8 @@
 """
 Simple BankAccount class demonstrating core OOP concepts.
+
+Reference:
+https://docs.python.org/3/tutorial/classes.html
 """
 
 

From 5e94a72b92687061ccfd9af9b378a4e02e2511a1 Mon Sep 17 00:00:00 2001
From: Nick Zerjeski <57059725+nickzerjeski@users.noreply.github.com>
Date: Tue, 14 Apr 2026 10:18:20 +0200
Subject: [PATCH 3/4] Update other/bank_account.py

Co-authored-by: Copilot <175728472+Copilot@users.noreply.github.com>
---
 other/bank_account.py | 25 +++++++++++++++++++++++++
 1 file changed, 25 insertions(+)

diff --git a/other/bank_account.py b/other/bank_account.py
index 6ada347d6240..f501ae07382f 100644
--- a/other/bank_account.py
+++ b/other/bank_account.py
@@ -19,6 +19,31 @@ class BankAccount:
     130.0
     >>> account.account_number
     'ACC-1001'
+
+    >>> BankAccount("", initial_balance=10.0)
+    Traceback (most recent call last):
+    ...
+    ValueError: account_number must be provided
+
+    >>> BankAccount("ACC-1002", initial_balance=-1.0)
+    Traceback (most recent call last):
+    ...
+    ValueError: initial_balance cannot be negative
+
+    >>> account.deposit(0)
+    Traceback (most recent call last):
+    ...
+    ValueError: deposit amount must be positive
+
+    >>> account.withdraw(0)
+    Traceback (most recent call last):
+    ...
+    ValueError: withdraw amount must be positive
+
+    >>> account.withdraw(1000)
+    Traceback (most recent call last):
+    ...
+    ValueError: insufficient funds
     """
 
     def __init__(self, account_number: str, initial_balance: float = 0.0) -> None:

From d28ec078bc353ad0f710ed9693291cf4f168a482 Mon Sep 17 00:00:00 2001
From: Nick Zerjeski <57059725+nickzerjeski@users.noreply.github.com>
Date: Tue, 14 Apr 2026 10:18:31 +0200
Subject: [PATCH 4/4] Update other/bank_account.py

Co-authored-by: Copilot <175728472+Copilot@users.noreply.github.com>
---
 other/bank_account.py | 14 ++++++++++++--
 1 file changed, 12 insertions(+), 2 deletions(-)

diff --git a/other/bank_account.py b/other/bank_account.py
index f501ae07382f..97137d21dc4a 100644
--- a/other/bank_account.py
+++ b/other/bank_account.py
@@ -2,14 +2,24 @@
 Simple BankAccount class demonstrating core OOP concepts.
 
 Reference:
-https://docs.python.org/3/tutorial/classes.html
+Invariant-preserving bank account state model.
+
+This module implements a minimal transactional data model whose computational
+value is the enforcement of account invariants during constant-time state
+transitions: account identifiers must be present, balances may not start
+negative, deposits must be positive, and withdrawals may not overdraw the
+account.
 """
 
 
 class BankAccount:
     """
-    Basic bank account model with encapsulated account number and balance.
+    Stateful account abstraction with validated balance updates.
 
+    The class is intentionally small, but its purpose is not to serve as a
+    generic OOP tutorial. It provides a compact example of how to model a
+    mutable record while preserving correctness constraints across operations,
+    with each transaction executing in O(1) time.
     >>> account = BankAccount("ACC-1001", initial_balance=100.0)
     >>> account.balance
     100.0