From a8734eca0d08b484154903bcd50fbb7d03c32294 Mon Sep 17 00:00:00 2001 From: Sergei Bezymyanniy Date: Sat, 10 Oct 2026 00:58:12 +0300 Subject: [PATCH] Solve task 2 --- src/part2/cart.py | 166 +++++++++++++++++++++++++++---------------- src/part2/crud.py | 159 +++++++++++++++++------------------------ src/part2/storage.py | 32 ++------- src/part2/utils.py | 27 ++----- 4 files changed, 177 insertions(+), 207 deletions(-) diff --git a/src/part2/cart.py b/src/part2/cart.py index 063f9aea..cbdaa539 100644 --- a/src/part2/cart.py +++ b/src/part2/cart.py @@ -1,18 +1,7 @@ -"""Shopping-cart operations layered on top of the product store. - -The cart is a plain list of tuples, one :data:`CartLine` -- -``(product_id, quantity)`` -- per distinct product. Moving units between the -store and the cart keeps the two sides in balance: :func:`add_to_cart` takes -units out of stock, :func:`remove_from_cart` puts them back. - -Like the CRUD layer, the failure path never raises -- the operation prints -an explanatory message to stdout and returns ``None``. -""" - from typing import Final -from .crud import read_product, update_product # noqa: F401 -from .storage import ( # noqa: F401 +from .crud import read_product, update_product +from .storage import ( NAME_INDEX, PRICE_INDEX, QUANTITY_INDEX, @@ -20,11 +9,22 @@ ) -type CartLine = tuple[int, int] +CartLine = tuple[int, int] + +LINE_PRODUCT_ID_INDEX: Final[int] = 0 +LINE_QUANTITY_INDEX: Final[int] = 1 + -# TODO: задайте позиции полей внутри кортежа CartLine -LINE_PRODUCT_ID_INDEX: Final = 0 -LINE_QUANTITY_INDEX: Final = 0 +def find_cart_line( + cart: list[CartLine], + product_id: int, +) -> CartLine | None: + for line in cart: + if line[LINE_PRODUCT_ID_INDEX] == product_id: + return line + + print(f"Product {product_id} is not in the cart") + return None def add_to_cart( @@ -33,28 +33,45 @@ def add_to_cart( product_id: int, quantity: int, ) -> CartLine | None: - """Move ``quantity`` units of ``product_id`` from the store into ``cart``. - - The product is looked up in ``storage``. If it is missing, a message is - printed (by :func:`~src.part2.crud.read_product`) and nothing - changes. If the store holds fewer units than requested, an explanatory - message is printed and nothing changes. Otherwise the store record is - decremented by ``quantity`` and the cart line for ``product_id`` gains - ``quantity`` units -- a new line is created when the cart had none. - - Args: - storage: The product store to draw stock from; modified in place on - success. - cart: The cart to add the units to; modified in place on success. - product_id: The identifier of the product to add. - quantity: Number of units to move into the cart. - - Returns: - The cart line for ``product_id`` after the addition, or ``None`` - when the product is unknown or the store cannot cover the request. - """ - # TODO: реализуйте функцию - return (0, 0) + product = read_product(storage, product_id) + + if product is None: + return None + + storage_quantity = product[QUANTITY_INDEX] + + if storage_quantity < quantity: + print( + f"Not enough stock for product {product_id}: " + f"{storage_quantity} available, " + f"{quantity} requested." + ) + return None + + new_fields = ( + product[NAME_INDEX], + product[PRICE_INDEX], + storage_quantity - quantity, + ) + + update_product( + storage, + product_id, + new_fields, + ) + + for index, line in enumerate(cart): + if line[LINE_PRODUCT_ID_INDEX] == product_id: + new_line = ( + product_id, + line[LINE_QUANTITY_INDEX] + quantity, + ) + cart[index] = new_line + return new_line + + new_line = (product_id, quantity) + cart.append(new_line) + return new_line def remove_from_cart( @@ -63,27 +80,50 @@ def remove_from_cart( product_id: int, quantity: int, ) -> CartLine | None: - """Move ``quantity`` units of ``product_id`` from ``cart`` back to the store. - - The cart line for ``product_id`` is looked up. If there is none, a - message is printed and nothing changes. If the line holds fewer units - than requested, an explanatory message is printed and nothing changes. - Otherwise the cart line loses ``quantity`` units -- the line is dropped - when it reaches zero -- and the store record gains ``quantity`` units - back. - - Args: - storage: The product store to return stock to; modified in place on - success. - cart: The cart to take the units from; modified in place on - success. - product_id: The identifier of the product to remove. - quantity: Number of units to move back into the store. - - Returns: - The cart line for ``product_id`` after the removal (a quantity of - zero means the line was dropped), or ``None`` when the cart has no - line for the product or holds too few units. - """ - # TODO: реализуйте функцию - return (0, 0) + cart_line = find_cart_line(cart, product_id) + + if cart_line is None: + return None + + if cart_line[LINE_QUANTITY_INDEX] < quantity: + print( + f"Cart holds only {cart_line[LINE_QUANTITY_INDEX]} " + f"unit(s) of product {product_id}, " + f"cannot remove {quantity}." + ) + return None + + product = read_product(storage, product_id) + + if product is None: + return None + + new_quantity = product[QUANTITY_INDEX] + quantity + + new_fields = ( + product[NAME_INDEX], + product[PRICE_INDEX], + new_quantity, + ) + + update_product( + storage, + product_id, + new_fields, + ) + + new_line: CartLine = ( + product_id, + cart_line[LINE_QUANTITY_INDEX] - quantity, + ) + + if new_line[LINE_QUANTITY_INDEX] == 0: + cart.remove(cart_line) + return new_line + + for index, line in enumerate(cart): + if line == cart_line: + cart[index] = new_line + return new_line + + return None diff --git a/src/part2/crud.py b/src/part2/crud.py index d026cbcb..a37746cc 100644 --- a/src/part2/crud.py +++ b/src/part2/crud.py @@ -1,79 +1,58 @@ -"""Create/read/update/delete operations over the in-memory product store. - -Every operation takes the store -- a list of -:data:`~src.part2.storage.Product` tuples -- as its first argument and -works on it in place. The failure path never raises: the operation prints -an explanatory message to stdout and returns ``None``. - -The identifier of a new product is derived from the store itself -(:func:`generate_product_id`): one past the greatest identifier in use, or -:data:`~src.part2.storage.PRODUCT_ID_MIN` when the store is empty. -Product names are kept unique -- :func:`create_product` refuses a name that -is already taken. -""" - from decimal import Decimal -from .storage import ( # noqa: F401 +from .storage import ( NAME_INDEX, PRODUCT_ID_INDEX, PRODUCT_ID_MIN, Product, ) -from .utils import normalize_price # noqa: F401 +from .utils import normalize_price -def generate_product_id(storage: list[Product]) -> int: - """Choose the identifier for the next product added to ``storage``. +def create_product( + storage: list[Product], + fields: tuple[str, Decimal, int], +) -> int | None: + product_name, product_price, product_quantity = fields - Args: - storage: The product store to inspect. + for product in storage: + if product_name == product[NAME_INDEX]: + print(f"Product name {product_name} is already taken.") + return None - Returns: - One past the greatest identifier currently held in ``storage``, or - :data:`~src.part2.storage.PRODUCT_ID_MIN` when ``storage`` is - empty. - """ - # TODO: реализуйте функцию - return 0 + product_id = generate_product_id(storage) + storage.append( + ( + product_id, + product_name, + normalize_price(product_price), + product_quantity, + ) + ) + + return product_id -def create_product( - storage: list[Product], fields: tuple[str, Decimal, int] -) -> int | None: - """Append a new product to ``storage`` and return its new identifier. - Args: - storage: The product store to append to; modified in place on - success. - fields: A ``(name, price, quantity)`` tuple describing the product. - ``price`` is a :class:`~decimal.Decimal` amount and is rounded - to the stored money precision before it is saved. +def generate_product_id(storage: list[Product]) -> int: + if not storage: + return PRODUCT_ID_MIN - Returns: - The identifier generated for the new product, or ``None`` when a - product with the same name already exists. In the ``None`` case - ``storage`` is left unchanged and a message naming the clashing - name is printed. - """ - # TODO: реализуйте функцию - return 0 + max_id = max(product[PRODUCT_ID_INDEX] for product in storage) + return max_id + 1 -def read_product(storage: list[Product], product_id: int) -> Product | None: - """Return the product stored under ``product_id``. - Args: - storage: The product store to search. - product_id: The identifier to look up. +def read_product( + storage: list[Product], + product_id: int, +) -> Product | None: + for product in storage: + if product[PRODUCT_ID_INDEX] == product_id: + return product - Returns: - The matching ``(product_id, name, price, quantity)`` record, or - ``None`` when no product carries that identifier (a message is - printed in that case). - """ - # TODO: реализуйте функцию - return (0, "", Decimal(0), 0) + print(f"No product with id {product_id}") + return None def update_product( @@ -81,40 +60,32 @@ def update_product( product_id: int, fields: tuple[str, Decimal, int], ) -> Product | None: - """Overwrite the fields of the product stored under ``product_id``. - - The identifier itself is preserved; only ``name``, ``price`` and - ``quantity`` are replaced. - - Args: - storage: The product store to modify; the matching record is - replaced in place on success. - product_id: The identifier of the product to change. - fields: A ``(name, price, quantity)`` tuple with the new values. - ``price`` is a :class:`~decimal.Decimal` amount and is rounded - to the stored money precision before it is saved. - - Returns: - The updated ``(product_id, name, price, quantity)`` record, or - ``None`` when no product carries that identifier (``storage`` is - left unchanged and a message is printed). - """ - # TODO: реализуйте функцию - return (0, "", Decimal(0), 0) - - -def delete_product(storage: list[Product], product_id: int) -> int | None: - """Remove the product stored under ``product_id`` from ``storage``. - - Args: - storage: The product store to remove from; modified in place on - success. - product_id: The identifier of the product to remove. - - Returns: - ``product_id`` when a product was removed, or ``None`` when no - product carried that identifier (``storage`` is left unchanged and - a message is printed). - """ - # TODO: реализуйте функцию - return 0 + for index, product in enumerate(storage): + if product[PRODUCT_ID_INDEX] == product_id: + new_name, new_price, new_quantity = fields + + new_product: Product = ( + product_id, + new_name, + normalize_price(new_price), + new_quantity, + ) + + storage[index] = new_product + return new_product + + print(f"No product with id {product_id}") + return None + + +def delete_product( + storage: list[Product], + product_id: int, +) -> int | None: + for index, product in enumerate(storage): + if product[PRODUCT_ID_INDEX] == product_id: + storage.pop(index) + return product_id + + print(f"No product with id {product_id}.") + return None diff --git a/src/part2/storage.py b/src/part2/storage.py index b63d5fc7..726ab823 100644 --- a/src/part2/storage.py +++ b/src/part2/storage.py @@ -1,34 +1,12 @@ -"""In-memory product store for the shop CRUD exercise. - -The store is deliberately primitive: a plain list of tuples, with no -persistence, no indexing and no schema enforcement. Each element is a -:data:`Product` record -- a ``(product_id, name, price, quantity)`` tuple -where: - -* ``product_id`` -- unique positive integer key, assigned by the create - operation in :mod:`src.part2.crud`; -* ``name`` -- human-readable product name, unique across the store; -* ``price`` -- price of a single unit, held as a :class:`~decimal.Decimal` - amount rounded to a fixed number of decimal places (see - :func:`src.part2.utils.normalize_price`) so that money is never - subject to binary floating-point error; -* ``quantity`` -- number of units currently in stock. - -Field positions are exposed as ``*_INDEX`` constants so callers never -hard-code tuple offsets. -""" - from decimal import Decimal from typing import Final -type Product = tuple[int, str, Decimal, int] +Product = tuple[int, str, Decimal, int] -# TODO: задайте позиции полей внутри кортежа Product PRODUCT_ID_INDEX: Final = 0 -NAME_INDEX: Final = 0 -PRICE_INDEX: Final = 0 -QUANTITY_INDEX: Final = 0 +NAME_INDEX: Final = 1 +PRICE_INDEX: Final = 2 +QUANTITY_INDEX: Final = 3 -# TODO: задайте идентификатор первого товара в пустом хранилище -PRODUCT_ID_MIN: Final[int] = 0 +PRODUCT_ID_MIN: Final[int] = 1 diff --git a/src/part2/utils.py b/src/part2/utils.py index 11bd7a76..28fe897f 100644 --- a/src/part2/utils.py +++ b/src/part2/utils.py @@ -1,29 +1,10 @@ -"""Standalone helpers shared by the part2 storage and CRUD modules. - -For now this is limited to money handling: :func:`normalize_price` rounds a -raw :class:`~decimal.Decimal` amount to the fixed number of fractional -digits (:data:`PRICE_PRECISION`) that every stored price uses, keeping -currency values free of binary floating-point error. -""" - -from decimal import ROUND_HALF_UP, Decimal # noqa: F401 +from decimal import ROUND_HALF_UP, Decimal from typing import Final -# TODO: задайте число знаков после запятой и шаг квантования -PRICE_PRECISION: Final[int] = 0 -PRICE_STEP: Final = Decimal(0) +PRICE_PRECISION: Final[int] = 2 +PRICE_STEP: Final[Decimal] = Decimal(1).scaleb(-PRICE_PRECISION) def normalize_price(price: Decimal) -> Decimal: - """Round a price to the precision every stored record uses. - - Args: - price: The raw price amount. - - Returns: - ``price`` quantised to :data:`PRICE_PRECISION` fractional digits, - with halves rounded up. - """ - # TODO: реализуйте функцию - return Decimal(0) + return price.quantize(PRICE_STEP, rounding=ROUND_HALF_UP)