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from __future__ import annotations from collections.abc import Sequence from typing import Any, Generic from typing_extensions import Self from langgraph._internal._typing import MISSING from langgraph.channels.base import BaseChannel, Value from langgraph.errors import EmptyChannelError, InvalidUpdateError __all__ = ("EphemeralValue",) class EphemeralValue(Generic[Value], BaseChannel[Value, Value, Value]): """Stores the value received in the step immediately preceding, clears after.""" __slots__ = ("value", "guard") value: Value | Any guard: bool def __init__(self, typ: Any, guard: bool = True) -> None: super().__init__(typ) self.guard = guard self.value = MISSING def __eq__(self, value: object) -> bool: return isinstance(value, EphemeralValue) and value.guard == self.guard @property def ValueType(self) -> type[Value]: """The type of the value stored in the channel.""" return self.typ @property def UpdateType(self) -> type[Value]: """The type of the update received by the channel.""" return self.typ def copy(self) -> Self: """Return a copy of the channel.""" empty = self.__class__(self.typ, self.guard) empty.key = self.key empty.value = self.value return empty def from_checkpoint(self, checkpoint: Value) -> Self: empty = self.__class__(self.typ, self.guard) empty.key = self.key if checkpoint is not MISSING: empty.value = checkpoint return empty def update(self, values: Sequence[Value]) -> bool: if len(values) == 0: if self.value is not MISSING: self.value = MISSING return True else: return False if len(values) != 1 and self.guard: raise InvalidUpdateError( f"At key '{self.key}': EphemeralValue(guard=True) can receive only one value per step. Use guard=False if you want to store any one of multiple values." ) self.value = values[-1] return True def get(self) -> Value: if self.value is MISSING: raise EmptyChannelError() return self.value def is_available(self) -> bool: return self.value is not MISSING def checkpoint(self) -> Value: return self.value