mirror of
https://github.com/langchain-ai/langgraph.git
synced 2026-09-29 21:15:11 +02:00
143 lines
4.2 KiB
Python
143 lines
4.2 KiB
Python
from abc import ABC, abstractmethod
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from contextlib import asynccontextmanager, contextmanager
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from datetime import datetime, timezone
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from typing import (
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Any,
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AsyncGenerator,
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Generator,
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Generic,
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Mapping,
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Optional,
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Sequence,
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TypeVar,
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)
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from typing_extensions import Self
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from langgraph.checkpoint.base import Checkpoint
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from langgraph.errors import EmptyChannelError, InvalidUpdateError
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Value = TypeVar("Value")
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Update = TypeVar("Update")
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C = TypeVar("C")
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class BaseChannel(Generic[Value, Update, C], ABC):
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@property
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@abstractmethod
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def ValueType(self) -> Any:
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"""The type of the value stored in the channel."""
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@property
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@abstractmethod
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def UpdateType(self) -> Any:
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"""The type of the update received by the channel."""
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# serialize/deserialize methods
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@abstractmethod
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def checkpoint(self) -> Optional[C]:
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"""Return a serializable representation of the channel's current state.
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Raises EmptyChannelError if the channel is empty (never updated yet),
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or doesn't support checkpoints."""
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@contextmanager
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@abstractmethod
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def from_checkpoint(
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self, checkpoint: Optional[C] = None
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) -> Generator[Self, None, None]:
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"""Return a new identical channel, optionally initialized from a checkpoint.
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If the checkpoint contains complex data structures, they should be copied."""
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@asynccontextmanager
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async def afrom_checkpoint(
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self, checkpoint: Optional[C] = None
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) -> AsyncGenerator[Self, None]:
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"""Return a new identical channel, optionally initialized from a checkpoint.
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If the checkpoint contains complex data structures, they should be copied."""
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with self.from_checkpoint(checkpoint) as value:
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yield value
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# state methods
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@abstractmethod
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def update(self, values: Sequence[Update]) -> None:
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"""Update the channel's value with the given sequence of updates.
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The order of the updates in the sequence is arbitrary.
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Raises InvalidUpdateError if the sequence of updates is invalid."""
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@abstractmethod
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def get(self) -> Value:
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"""Return the current value of the channel.
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Raises EmptyChannelError if the channel is empty (never updated yet)."""
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@contextmanager
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def ChannelsManager(
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channels: Mapping[str, BaseChannel],
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checkpoint: Checkpoint,
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) -> Generator[Mapping[str, BaseChannel], None, None]:
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"""Manage channels for the lifetime of a Pregel invocation (multiple steps)."""
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# TODO use https://docs.python.org/3/library/contextlib.html#contextlib.ExitStack
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empty = {
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k: v.from_checkpoint(checkpoint["channel_values"].get(k))
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for k, v in channels.items()
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}
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try:
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yield {k: v.__enter__() for k, v in empty.items()}
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finally:
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for v in empty.values():
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v.__exit__(None, None, None)
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@asynccontextmanager
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async def AsyncChannelsManager(
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channels: Mapping[str, BaseChannel],
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checkpoint: Checkpoint,
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) -> AsyncGenerator[Mapping[str, BaseChannel], None]:
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"""Manage channels for the lifetime of a Pregel invocation (multiple steps)."""
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empty = {
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k: v.afrom_checkpoint(checkpoint["channel_values"].get(k))
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for k, v in channels.items()
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}
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try:
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yield {k: await v.__aenter__() for k, v in empty.items()}
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finally:
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for v in empty.values():
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await v.__aexit__(None, None, None)
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def create_checkpoint(
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checkpoint: Checkpoint, channels: Mapping[str, BaseChannel]
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) -> Checkpoint:
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"""Create a checkpoint for the given channels."""
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ts = datetime.now(timezone.utc).isoformat()
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assert (
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ts > checkpoint["ts"]
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), f"Timestamps must be monotonically increasing, got {ts} <= {checkpoint['ts']}"
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values: dict[str, Any] = {}
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for k, v in channels.items():
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try:
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values[k] = v.checkpoint()
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except EmptyChannelError:
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pass
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return Checkpoint(
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v=1,
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ts=ts,
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channel_values=values,
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channel_versions=checkpoint["channel_versions"],
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versions_seen=checkpoint["versions_seen"],
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)
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__all__ = [
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"BaseChannel",
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"ChannelsManager",
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"AsyncChannelsManager",
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"create_checkpoint",
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"EmptyChannelError",
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"InvalidUpdateError",
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]
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