5. Безымянный Сергей Андреевич. 613

src/part5/cart.py

@@ -1,18 +1,4 @@
-"""Shopping-cart operations layered on top of the product store.
-
-The cart is a plain dictionary mapping each product identifier to the
-number of units of that product in the cart. 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 .storage import Product
-
-
-# TODO: при необходимости добавьте свои вспомогательные функции
+from .storage import QUANTITY_KEY, Product
 
 
 def add_to_cart(
@@ -22,33 +8,22 @@ def add_to_cart(
     product_id: int,
     quantity: int,
 ) -> int | None:
-    """Move ``quantity`` units of ``product_id`` from the store into ``cart``.
+    if product_id not in storage:
+        print(f"no product with id {product_id}")
+        return None
 
-    The product is looked up in ``storage``. If it is missing, a message is
-    printed (by :func:`~src.part5.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 gains ``quantity`` units of
-    ``product_id`` -- the product is added when the cart had none of it.
+    storage_quantity = storage[product_id][QUANTITY_KEY]
+    if quantity > storage_quantity:
+        print(
+            f"not enough stock for product {product_id}: "
+            f"{storage_quantity} available, {quantity} requested"
+        )
+        return None
 
-    Args:
-        storage: The product store to draw stock from; modified in place on
-            success.
-        product_names: The normalised names in ``storage``; threaded
-            through to :func:`~src.part5.crud.update_product`, which
-            keeps it in sync (a quantity-only update never renames a
-            product, so it is left unchanged here).
-        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.
+    storage[product_id][QUANTITY_KEY] -= quantity
+    cart[product_id] = cart.get(product_id, 0) + quantity
 
-    Returns:
-        The quantity of ``product_id`` in the cart after the addition, or
-        ``None`` when the product is unknown or the store cannot cover the
-        request.
-    """
-    # TODO: реализуйте функцию (используйте своё решение части 4)
-    return 0
+    return cart[product_id]
 
 
 def remove_from_cart(
@@ -58,31 +33,27 @@ def remove_from_cart(
     product_id: int,
     quantity: int,
 ) -> int | None:
-    """Move ``quantity`` units of ``product_id`` from ``cart`` back to the store.
-
-    If the cart holds no units of ``product_id``, a message is printed and
-    nothing changes. If it holds fewer units than requested, an explanatory
-    message is printed and nothing changes. Otherwise the cart loses
-    ``quantity`` units of the product -- the product is dropped from the
-    cart when its quantity reaches zero -- and the store record gains
-    ``quantity`` units back.
-
-    Args:
-        storage: The product store to return stock to; modified in place on
-            success.
-        product_names: The normalised names in ``storage``; threaded
-            through to :func:`~src.part5.crud.update_product`, which
-            keeps it in sync (a quantity-only update never renames a
-            product, so it is left unchanged here).
-        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 quantity of ``product_id`` left in the cart after the removal
-        (zero means the product was dropped from the cart), or ``None`` when
-        the cart does not hold the product or holds too few units.
-    """
-    # TODO: реализуйте функцию (используйте своё решение части 4)
-    return 0
+    if product_id not in cart:
+        print(f"product {product_id} is not in the cart")
+        return None
+
+    cart_quantity = cart[product_id]
+    if quantity > cart_quantity:
+        print(
+            f"cart holds only {cart_quantity} unit(s) of product {product_id},"
+            f" cannot remove {quantity}"
+        )
+        return None
+
+    if product_id not in storage:
+        print(f"no product with id {product_id}")
+        return None
+
+    storage[product_id][QUANTITY_KEY] += quantity
+    cart[product_id] -= quantity
+
+    if cart[product_id] == 0:
+        del cart[product_id]
+        return 0
+
+    return cart[product_id]

src/part5/constants.py

@@ -1,37 +1,11 @@
-"""Bit layout and default epoch for the Twitter Snowflake ID generator.
-
-A Snowflake identifier is a 63-bit positive integer packed as follows, from
-the most significant bit downwards:
-
-    1 bit   unused sign bit, always zero
-    41 bits milliseconds elapsed since a custom epoch
-    10 bits node identifier
-    12 bits per-millisecond sequence counter
-
-The shift and mask constants should be derived from the bit widths so that
-changing a width keeps everything else consistent.
-"""
-
 from typing import Final
 
 
-# TODO: замените заглушки (0) на корректные значения (используйте своё решение
-# части 1).
-
-# Twitter's original Snowflake epoch: 2010-11-04 01:42:54.657 UTC.
-EPOCH_MS_DEFAULT: Final[int] = 0
-
-# Node identifier used when the caller does not supply one.
-NODE_ID_DEFAULT: Final[int] = 0
-
-# Width of each field, in bits.
-TIMESTAMP_BITS: Final[int] = 0
-NODE_ID_BITS: Final[int] = 0
-SEQUENCE_ID_BITS: Final[int] = 0
-
-# Largest value each field can hold.
-TIMESTAMP_MS_MAX: Final[int] = 0
-NODE_ID_MAX: Final[int] = 0
-SEQUENCE_ID_MAX: Final[int] = 0
-
-# Здесь можно добавить собственные вспомогательные константы
+EPOCH_MS_DEFAULT: Final[int] = 1288834974657
+NODE_ID_DEFAULT: Final[int] = 1
+TIMESTAMP_BITS: Final[int] = 41
+NODE_ID_BITS: Final[int] = 10
+SEQUENCE_ID_BITS: Final[int] = 12
+TIMESTAMP_MS_MAX: Final[int] = 2**TIMESTAMP_BITS - 1
+NODE_ID_MAX: Final[int] = 2**NODE_ID_BITS - 1
+SEQUENCE_ID_MAX: Final[int] = 2**SEQUENCE_ID_BITS - 1