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from __future__ import annotations from collections.abc import Sequence from typing import ( Any, Callable, NamedTuple, Optional, TypeVar, Union, cast, ) from langchain_core.runnables import Runnable, RunnableConfig from langgraph._internal._constants import CONF, CONFIG_KEY_SEND, TASKS from langgraph._internal._runnable import RunnableCallable from langgraph._internal._typing import MISSING from langgraph.errors import InvalidUpdateError from langgraph.types import Send TYPE_SEND = Callable[[Sequence[tuple[str, Any]]], None] R = TypeVar("R", bound=Runnable) SKIP_WRITE = object() PASSTHROUGH = object() class ChannelWriteEntry(NamedTuple): channel: str """Channel name to write to.""" value: Any = PASSTHROUGH """Value to write, or PASSTHROUGH to use the input.""" skip_none: bool = False """Whether to skip writing if the value is None.""" mapper: Callable | None = None """Function to transform the value before writing.""" class ChannelWriteTupleEntry(NamedTuple): mapper: Callable[[Any], Sequence[tuple[str, Any]] | None] """Function to extract tuples from value.""" value: Any = PASSTHROUGH """Value to write, or PASSTHROUGH to use the input.""" static: Sequence[tuple[str, Any, str | None]] | None = None """Optional, declared writes for static analysis.""" class ChannelWrite(RunnableCallable): """Implements the logic for sending writes to CONFIG_KEY_SEND. Can be used as a runnable or as a static method to call imperatively.""" writes: list[ChannelWriteEntry | ChannelWriteTupleEntry | Send] """Sequence of write entries or Send objects to write.""" def __init__( self, writes: Sequence[ChannelWriteEntry | ChannelWriteTupleEntry | Send], *, tags: Sequence[str] | None = None, ): super().__init__( func=self._write, afunc=self._awrite, name=None, tags=tags, trace=False, ) self.writes = cast( list[Union[ChannelWriteEntry, ChannelWriteTupleEntry, Send]], writes ) def get_name(self, suffix: str | None = None, *, name: str | None = None) -> str: if not name: name = f"ChannelWrite<{','.join(w.channel if isinstance(w, ChannelWriteEntry) else '...' if isinstance(w, ChannelWriteTupleEntry) else w.node for w in self.writes)}>" return super().get_name(suffix, name=name) def _write(self, input: Any, config: RunnableConfig) -> None: writes = [ ChannelWriteEntry(write.channel, input, write.skip_none, write.mapper) if isinstance(write, ChannelWriteEntry) and write.value is PASSTHROUGH else ChannelWriteTupleEntry(write.mapper, input) if isinstance(write, ChannelWriteTupleEntry) and write.value is PASSTHROUGH else write for write in self.writes ] self.do_write( config, writes, ) return input async def _awrite(self, input: Any, config: RunnableConfig) -> None: writes = [ ChannelWriteEntry(write.channel, input, write.skip_none, write.mapper) if isinstance(write, ChannelWriteEntry) and write.value is PASSTHROUGH else ChannelWriteTupleEntry(write.mapper, input) if isinstance(write, ChannelWriteTupleEntry) and write.value is PASSTHROUGH else write for write in self.writes ] self.do_write( config, writes, ) return input @staticmethod def do_write( config: RunnableConfig, writes: Sequence[ChannelWriteEntry | ChannelWriteTupleEntry | Send], allow_passthrough: bool = True, ) -> None: # validate for w in writes: if isinstance(w, ChannelWriteEntry): if w.channel == TASKS: raise InvalidUpdateError( "Cannot write to the reserved channel TASKS" ) if w.value is PASSTHROUGH and not allow_passthrough: raise InvalidUpdateError("PASSTHROUGH value must be replaced") if isinstance(w, ChannelWriteTupleEntry): if w.value is PASSTHROUGH and not allow_passthrough: raise InvalidUpdateError("PASSTHROUGH value must be replaced") # if we want to persist writes found before hitting a ParentCommand # can move this to a finally block write: TYPE_SEND = config[CONF][CONFIG_KEY_SEND] write(_assemble_writes(writes)) @staticmethod def is_writer(runnable: Runnable) -> bool: """Used by PregelNode to distinguish between writers and other runnables.""" return ( isinstance(runnable, ChannelWrite) or getattr(runnable, "_is_channel_writer", MISSING) is not MISSING ) @staticmethod def get_static_writes( runnable: Runnable, ) -> Sequence[tuple[str, Any, str | None]] | None: """Used to get conditional writes a writer declares for static analysis.""" if isinstance(runnable, ChannelWrite): return [ w for entry in runnable.writes if isinstance(entry, ChannelWriteTupleEntry) and entry.static for w in entry.static ] or None elif writes := getattr(runnable, "_is_channel_writer", MISSING): if writes is not MISSING: writes = cast( Sequence[tuple[Union[ChannelWriteEntry, Send], Optional[str]]], writes, ) entries = [e for e, _ in writes] labels = [la for _, la in writes] return [(*t, la) for t, la in zip(_assemble_writes(entries), labels)] @staticmethod def register_writer( runnable: R, static: Sequence[tuple[ChannelWriteEntry | Send, str | None]] | None = None, ) -> R: """Used to mark a runnable as a writer, so that it can be detected by is_writer. Instances of ChannelWrite are automatically marked as writers. Optionally, a list of declared writes can be passed for static analysis.""" # using object.__setattr__ to work around objects that override __setattr__ # eg. pydantic models and dataclasses object.__setattr__(runnable, "_is_channel_writer", static) return runnable def _assemble_writes( writes: Sequence[ChannelWriteEntry | ChannelWriteTupleEntry | Send], ) -> list[tuple[str, Any]]: """Assembles the writes into a list of tuples.""" tuples: list[tuple[str, Any]] = [] for w in writes: if isinstance(w, Send): tuples.append((TASKS, w)) elif isinstance(w, ChannelWriteTupleEntry): if ww := w.mapper(w.value): tuples.extend(ww) elif isinstance(w, ChannelWriteEntry): value = w.mapper(w.value) if w.mapper is not None else w.value if value is SKIP_WRITE: continue if w.skip_none and value is None: continue tuples.append((w.channel, value)) else: raise ValueError(f"Invalid write entry: {w}") return tuples