feat(other): add grocery store cart model (v3)

other/grocery_store_cart.py

@@ -0,0 +1,83 @@
+"""
+Console-free grocery cart logic.
+"""
+
+
+class GroceryStoreCart:
+    """
+    Maintain cart item quantities and compute totals.
+
+    >>> cart = GroceryStoreCart({"apple": 1.5, "milk": 2.0})
+    >>> cart.add_item("apple", 2)
+    >>> cart.add_item("milk")
+    >>> round(cart.total_price(), 2)
+    5.0
+    >>> cart.remove_item("apple")
+    >>> round(cart.total_price(), 2)
+    3.5
+
+    >>> GroceryStoreCart({})
+    Traceback (most recent call last):
+    ...
+    ValueError: price_catalog cannot be empty
+
+    >>> cart.add_item("bread")
+    Traceback (most recent call last):
+    ...
+    KeyError: "'bread' is not in the catalog"
+
+    >>> cart.add_item("apple", 0)
+    Traceback (most recent call last):
+    ...
+    ValueError: quantity must be positive
+
+    >>> cart.remove_item("milk", 0)
+    Traceback (most recent call last):
+    ...
+    ValueError: quantity must be positive
+
+    >>> empty_cart = GroceryStoreCart({"apple": 1.5})
+    >>> empty_cart.remove_item("apple")
+    Traceback (most recent call last):
+    ...
+    KeyError: "'apple' is not present in the cart"
+    """
+
+    def __init__(self, price_catalog: dict[str, float]) -> None:
+        if not price_catalog:
+            raise ValueError("price_catalog cannot be empty")
+        self.price_catalog = dict(price_catalog)
+        self.quantities: dict[str, int] = {}
+
+    def add_item(self, item: str, quantity: int = 1) -> None:
+        if item not in self.price_catalog:
+            msg = f"{item!r} is not in the catalog"
+            raise KeyError(msg)
+        if quantity <= 0:
+            raise ValueError("quantity must be positive")
+        self.quantities[item] = self.quantities.get(item, 0) + quantity
+
+    def remove_item(self, item: str, quantity: int = 1) -> None:
+        if quantity <= 0:
+            raise ValueError("quantity must be positive")
+        current = self.quantities.get(item, 0)
+        if current == 0:
+            msg = f"{item!r} is not present in the cart"
+            raise KeyError(msg)
+        if quantity > current:
+            raise ValueError("quantity exceeds amount present in the cart")
+        if (remaining := current - quantity) > 0:
+            self.quantities[item] = remaining
+        else:
+            self.quantities.pop(item, None)
+
+    def total_price(self) -> float:
+        return sum(
+            self.price_catalog[item] * qty for item, qty in self.quantities.items()
+        )
+
+
+if __name__ == "__main__":
+    import doctest
+
+    doctest.testmod()