From b88130b19708e329bd09b0f75528fada01c869a5 Mon Sep 17 00:00:00 2001 From: Luminol Date: Fri, 25 Sep 2026 21:27:24 +0300 Subject: [PATCH 1/4] Solve task 1 --- src/part1/__init__.py | 1 - src/part1/constants.py | 36 +++---------- src/part1/snowflake.py | 118 ++++++++++------------------------------- 3 files changed, 37 insertions(+), 118 deletions(-) diff --git a/src/part1/__init__.py b/src/part1/__init__.py index 242b07ce..e69de29b 100644 --- a/src/part1/__init__.py +++ b/src/part1/__init__.py @@ -1 +0,0 @@ -"""Homework 3: a Twitter Snowflake identifier generator and its bit layout.""" diff --git a/src/part1/constants.py b/src/part1/constants.py index 9abfbba2..b4be5cc4 100644 --- a/src/part1/constants.py +++ b/src/part1/constants.py @@ -1,38 +1,18 @@ -"""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, см. TASK.md. -# Все константы, зависящие от ёмкостей *_BITS, должны вычисляться из них. - # Twitter's original Snowflake epoch: 2010-11-04 01:42:54.657 UTC. -EPOCH_MS_DEFAULT: Final[int] = 0 +EPOCH_MS_DEFAULT: Final[int] = 1288834974657 # Node identifier used when the caller does not supply one. -NODE_ID_DEFAULT: Final[int] = 0 +NODE_ID_DEFAULT: Final[int] = 1 # Width of each field, in bits. -TIMESTAMP_BITS: Final[int] = 0 -NODE_ID_BITS: Final[int] = 0 -SEQUENCE_ID_BITS: Final[int] = 0 +TIMESTAMP_BITS: Final[int] = 41 +NODE_ID_BITS: Final[int] = 10 +SEQUENCE_ID_BITS: Final[int] = 12 # 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 -# (например, сдвиги полей при сборке идентификатора). +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 diff --git a/src/part1/snowflake.py b/src/part1/snowflake.py index d3abf050..88c004a3 100644 --- a/src/part1/snowflake.py +++ b/src/part1/snowflake.py @@ -1,21 +1,6 @@ -"""Twitter Snowflake identifier generator. +import time -Snowflake produces roughly time-ordered 64-bit integer identifiers without -coordination between nodes. Each identifier packs the milliseconds elapsed -since a custom epoch, a node identifier and a per-millisecond sequence counter -into a single 63-bit positive integer (see ``constants`` for the layout). - -The public entry point is :func:`generate_snowflake_id`. It is stateless: the -caller passes the sequence counter on every call and is responsible for -advancing it within a millisecond and resetting it when the clock ticks over. - -Each packed field can be read back on its own with :func:`decode_timestamp_ms`, -:func:`decode_node_id` and :func:`decode_sequence_id`. -""" - -import time # noqa: F401 - -from .constants import ( # noqa: F401 +from .constants import ( EPOCH_MS_DEFAULT, NODE_ID_DEFAULT, NODE_ID_MAX, @@ -24,62 +9,23 @@ ) -def read_current_millis(epoch_ms: int) -> int: - """Read the number of milliseconds elapsed since the custom epoch. - - Args: - epoch_ms: The custom epoch expressed as Unix milliseconds. - - Returns: - The count of whole milliseconds between ``epoch_ms`` and now. May be - negative if ``epoch_ms`` lies in the future. - """ - # TODO: реализуйте функцию - return 0 +def read_current_millis(epoch_ms: int = EPOCH_MS_DEFAULT) -> int: + return time.time_ns() // 1_000_000 - epoch_ms def decode_timestamp_ms(snowflake_id: int, epoch_ms: int = EPOCH_MS_DEFAULT) -> int: - """Read the timestamp field out of a Snowflake identifier. - - Args: - snowflake_id: An identifier produced against the same epoch. - epoch_ms: The epoch the identifier was generated against. Defaults to - the original Twitter epoch (2010-11-04 01:42:54.657 UTC). - - Returns: - The absolute Unix time in milliseconds at which the identifier was - generated. - """ - # TODO: реализуйте функцию - return 0 + current_time = (snowflake_id >> (NODE_ID_MAX + SEQUENCE_ID_MAX)) + epoch_ms + return current_time def decode_node_id(snowflake_id: int) -> int: - """Read the node identifier field out of a Snowflake identifier. - - Args: - snowflake_id: An identifier produced by :func:`generate_snowflake_id`. - - Returns: - The node identifier packed into ``snowflake_id``, in the range - ``[0, NODE_ID_MAX]``. - """ - # TODO: реализуйте функцию - return 0 + node_id = (snowflake_id >> SEQUENCE_ID_MAX) & NODE_ID_MAX + return node_id def decode_sequence_id(snowflake_id: int) -> int: - """Read the sequence counter field out of a Snowflake identifier. - - Args: - snowflake_id: An identifier produced by :func:`generate_snowflake_id`. - - Returns: - The per-millisecond sequence counter packed into ``snowflake_id``, in - the range ``[0, SEQUENCE_ID_MAX]``. - """ - # TODO: реализуйте функцию - return 0 + sequence_id = snowflake_id & SEQUENCE_ID_MAX + return sequence_id def generate_snowflake_id( @@ -87,28 +33,22 @@ def generate_snowflake_id( node_id: int = NODE_ID_DEFAULT, epoch_ms: int = EPOCH_MS_DEFAULT, ) -> int | None: - """Build and return a Snowflake identifier for the current millisecond. - - The function is stateless: the caller passes the per-millisecond sequence - counter explicitly. It is the caller's responsibility to increment - ``sequence_id`` for identifiers minted within the same millisecond and to - reset it once the clock advances. - - Args: - sequence_id: The per-millisecond sequence counter, in the range - ``[0, SEQUENCE_ID_MAX]``. - node_id: The identifier of this node, in the range ``[0, NODE_ID_MAX]``. - Optional; defaults to ``NODE_ID_DEFAULT``. - epoch_ms: The start of the epoch as Unix milliseconds. Optional; - defaults to the original Twitter epoch (2010-11-04 01:42:54.657 - UTC). - - Returns: - The Snowflake identifier as a positive 63-bit integer, or ``None`` if - ``node_id`` is outside ``[0, NODE_ID_MAX]``, ``sequence_id`` is outside - ``[0, SEQUENCE_ID_MAX]``, or the elapsed time no longer fits in the - timestamp field (roughly 69 years after ``epoch_ms``). In each of those - cases an explanatory message is printed to stdout first. - """ - # TODO: реализуйте функцию - return 0 + if not (0 <= node_id <= NODE_ID_MAX): + print(f"node_id must be in [0, {NODE_ID_MAX}], current node_id is {node_id}") + return None + elif not (0 <= sequence_id <= SEQUENCE_ID_MAX): + print( + f"sequence_id must be in [0, {SEQUENCE_ID_MAX}], current sequence_id is {sequence_id}" + ) + return None + else: + if epoch_ms <= read_current_millis(epoch_ms) <= TIMESTAMP_MS_MAX: + snowflake_id = ( + (read_current_millis(epoch_ms) << (NODE_ID_MAX + SEQUENCE_ID_MAX)) + | (node_id << (SEQUENCE_ID_MAX)) + | sequence_id + ) + return snowflake_id + else: + print("overflows") + return None From 2ae02ddf04f643936610140d29396116dba4971a Mon Sep 17 00:00:00 2001 From: Luminol Date: Fri, 25 Sep 2026 23:40:07 +0300 Subject: [PATCH 2/4] Solve task 1 --- src/part1/snowflake.py | 10 ++++++---- 1 file changed, 6 insertions(+), 4 deletions(-) diff --git a/src/part1/snowflake.py b/src/part1/snowflake.py index 88c004a3..a56ced14 100644 --- a/src/part1/snowflake.py +++ b/src/part1/snowflake.py @@ -2,8 +2,10 @@ from .constants import ( EPOCH_MS_DEFAULT, + NODE_ID_BITS, NODE_ID_DEFAULT, NODE_ID_MAX, + SEQUENCE_ID_BITS, SEQUENCE_ID_MAX, TIMESTAMP_MS_MAX, ) @@ -14,12 +16,12 @@ def read_current_millis(epoch_ms: int = EPOCH_MS_DEFAULT) -> int: def decode_timestamp_ms(snowflake_id: int, epoch_ms: int = EPOCH_MS_DEFAULT) -> int: - current_time = (snowflake_id >> (NODE_ID_MAX + SEQUENCE_ID_MAX)) + epoch_ms + current_time = (snowflake_id >> (NODE_ID_BITS + SEQUENCE_ID_BITS)) + epoch_ms return current_time def decode_node_id(snowflake_id: int) -> int: - node_id = (snowflake_id >> SEQUENCE_ID_MAX) & NODE_ID_MAX + node_id = (snowflake_id >> SEQUENCE_ID_BITS) & NODE_ID_MAX return node_id @@ -44,8 +46,8 @@ def generate_snowflake_id( else: if epoch_ms <= read_current_millis(epoch_ms) <= TIMESTAMP_MS_MAX: snowflake_id = ( - (read_current_millis(epoch_ms) << (NODE_ID_MAX + SEQUENCE_ID_MAX)) - | (node_id << (SEQUENCE_ID_MAX)) + (read_current_millis(epoch_ms) << (NODE_ID_BITS + SEQUENCE_ID_BITS)) + | (node_id << (SEQUENCE_ID_BITS)) | sequence_id ) return snowflake_id From 6f0c39f91b587f3d3eb1e2f20bda2b5ceaceb86c Mon Sep 17 00:00:00 2001 From: Luminol Date: Fri, 2 Oct 2026 23:23:25 +0300 Subject: [PATCH 3/4] Solve task 2 --- src/part2/cart.py | 136 ++++++++++++++++++++++++------------------- src/part2/crud.py | 130 ++++++++++++++--------------------------- src/part2/storage.py | 30 ++-------- src/part2/utils.py | 28 ++------- 4 files changed, 130 insertions(+), 194 deletions(-) diff --git a/src/part2/cart.py b/src/part2/cart.py index 063f9aea..88cd6789 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, @@ -22,9 +11,17 @@ type CartLine = tuple[int, int] -# TODO: задайте позиции полей внутри кортежа CartLine + LINE_PRODUCT_ID_INDEX: Final = 0 -LINE_QUANTITY_INDEX: Final = 0 +LINE_QUANTITY_INDEX: Final = 1 + + +def find_cart_line(cart: list[CartLine], product_id: int) -> int | None: + for cartline in cart: + if cartline[LINE_PRODUCT_ID_INDEX] == product_id: + return cart.index(cartline) + + return None def add_to_cart( @@ -33,28 +30,34 @@ 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 quantity > storage_quantity: + print( + f"not enough stock for product {product_id}: {product[QUANTITY_INDEX]} available, {quantity} requested" + ) + return None + + fields = ( + product[NAME_INDEX], + product[PRICE_INDEX], + product[QUANTITY_INDEX] - quantity, + ) + + update_product(storage, product_id, fields) + + line_index = find_cart_line(cart, product_id) + if line_index is not None: + line: CartLine = (product_id, cart[line_index][LINE_QUANTITY_INDEX] + quantity) + return cart[line_index] + + line = (product_id, quantity) + cart.append(line) + + return line def remove_from_cart( @@ -63,27 +66,38 @@ 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) + line_index = find_cart_line(cart, product_id) + if line_index is None: + print(f"{product_id} is not in the cart") + return None + + line = cart[line_index] + if line[LINE_QUANTITY_INDEX] < quantity: + print( + f"cart holds only {line[LINE_QUANTITY_INDEX]} unit(s) of product {product_id}, cannot remove {quantity}" + ) + return None + + product = read_product(storage, product_id) + if product is None: + return None + + fields = ( + product[NAME_INDEX], + product[PRICE_INDEX], + product[QUANTITY_INDEX] + quantity, + ) + + update_product(storage, product_id, fields) + + line_index = find_cart_line(cart, product_id) + + if line_index is not None: + new_quantity = cart[line_index][LINE_QUANTITY_INDEX] - quantity + + new_line = (product_id, new_quantity) + + if new_quantity == 0 and line_index is not None: + del cart[line_index] + + return new_line diff --git a/src/part2/crud.py b/src/part2/crud.py index d026cbcb..114931c6 100644 --- a/src/part2/crud.py +++ b/src/part2/crud.py @@ -1,79 +1,55 @@ -"""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``. + if not storage: + return PRODUCT_ID_MIN + else: + return max(storage)[PRODUCT_ID_INDEX] + 1 - Args: - storage: The product store to inspect. - 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 +def product_search(storage: list[Product], product_id: int) -> Product | None: + for product in storage: + if product[PRODUCT_ID_INDEX] == product_id: + return product + + return None def create_product( storage: list[Product], fields: tuple[str, Decimal, int] ) -> int | None: - """Append a new product to ``storage`` and return its new identifier. + name, price, quantity = fields - 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. + for product in storage: + if name == product[NAME_INDEX]: + print(f"product name {name} is already taken") + return None - 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 + product_id = generate_product_id(storage) + product_price = normalize_price(price) + new_product: Product = (product_id, name, product_price, quantity) + storage.append(new_product) -def read_product(storage: list[Product], product_id: int) -> Product | None: - """Return the product stored under ``product_id``. + return product_id - Args: - storage: The product store to search. - product_id: The identifier to look up. - 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) +def read_product(storage: list[Product], product_id: int) -> Product | None: + product = product_search(storage, product_id) + if product is Product: + return product + + print(f"no product with id {product_id}") + return None def update_product( @@ -81,40 +57,24 @@ def update_product( product_id: int, fields: tuple[str, Decimal, int], ) -> Product | None: - """Overwrite the fields of the product stored under ``product_id``. + name, price, quantity = fields - The identifier itself is preserved; only ``name``, ``price`` and - ``quantity`` are replaced. + product = product_search(storage, product_id) + if product is not None: + new_price = normalize_price(price) + new_product = (product_id, name, new_price, quantity) + storage[storage.index(product)] = new_product + return new_product - 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) + print(f"no product with id {product_id}") + return None 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 + product = product_search(storage, product_id) + if product is not None: + storage.remove(product) + 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..81651a75 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] -# 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 ec0348d3..ff03fdfb 100644 --- a/src/part2/utils.py +++ b/src/part2/utils.py @@ -1,29 +1,13 @@ -"""Standalone helpers shared by the hw4 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(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. + """Для себя: метод number.quantize(step, rounding=round) округляет число + до состояния number.step знаков после запятой с точностью округления round """ - # TODO: реализуйте функцию - return Decimal(0) + return price.quantize(PRICE_STEP, rounding=ROUND_HALF_UP) From 1383f78c011afc08794a1d29916a9d299b0cd5c4 Mon Sep 17 00:00:00 2001 From: Luminol Date: Fri, 2 Oct 2026 23:26:49 +0300 Subject: [PATCH 4/4] Solve task 2 --- src/part2/crud.py | 2 +- 1 file changed, 1 insertion(+), 1 deletion(-) diff --git a/src/part2/crud.py b/src/part2/crud.py index 114931c6..8ef06ee0 100644 --- a/src/part2/crud.py +++ b/src/part2/crud.py @@ -45,7 +45,7 @@ def create_product( def read_product(storage: list[Product], product_id: int) -> Product | None: product = product_search(storage, product_id) - if product is Product: + if product is not None: return product print(f"no product with id {product_id}")