Source code for langchain.callbacks.streaming_stdout_final_only

"""Callback Handler streams to stdout on new llm token."""
import sys
from typing import Any, Dict, List, Optional

from langchain_core.callbacks import StreamingStdOutCallbackHandler

DEFAULT_ANSWER_PREFIX_TOKENS = ["Final", "Answer", ":"]

[docs]class FinalStreamingStdOutCallbackHandler(StreamingStdOutCallbackHandler): """Callback handler for streaming in agents. Only works with agents using LLMs that support streaming. Only the final output of the agent will be streamed. """
[docs] def append_to_last_tokens(self, token: str) -> None: self.last_tokens.append(token) self.last_tokens_stripped.append(token.strip()) if len(self.last_tokens) > len(self.answer_prefix_tokens): self.last_tokens.pop(0) self.last_tokens_stripped.pop(0)
[docs] def check_if_answer_reached(self) -> bool: if self.strip_tokens: return self.last_tokens_stripped == self.answer_prefix_tokens_stripped else: return self.last_tokens == self.answer_prefix_tokens
[docs] def __init__( self, *, answer_prefix_tokens: Optional[List[str]] = None, strip_tokens: bool = True, stream_prefix: bool = False, ) -> None: """Instantiate FinalStreamingStdOutCallbackHandler. Args: answer_prefix_tokens: Token sequence that prefixes the answer. Default is ["Final", "Answer", ":"] strip_tokens: Ignore white spaces and new lines when comparing answer_prefix_tokens to last tokens? (to determine if answer has been reached) stream_prefix: Should answer prefix itself also be streamed? """ super().__init__() if answer_prefix_tokens is None: self.answer_prefix_tokens = DEFAULT_ANSWER_PREFIX_TOKENS else: self.answer_prefix_tokens = answer_prefix_tokens if strip_tokens: self.answer_prefix_tokens_stripped = [ token.strip() for token in self.answer_prefix_tokens ] else: self.answer_prefix_tokens_stripped = self.answer_prefix_tokens self.last_tokens = [""] * len(self.answer_prefix_tokens) self.last_tokens_stripped = [""] * len(self.answer_prefix_tokens) self.strip_tokens = strip_tokens self.stream_prefix = stream_prefix self.answer_reached = False
[docs] def on_llm_start( self, serialized: Dict[str, Any], prompts: List[str], **kwargs: Any ) -> None: """Run when LLM starts running.""" self.answer_reached = False
[docs] def on_llm_new_token(self, token: str, **kwargs: Any) -> None: """Run on new LLM token. Only available when streaming is enabled.""" # Remember the last n tokens, where n = len(answer_prefix_tokens) self.append_to_last_tokens(token) # Check if the last n tokens match the answer_prefix_tokens list ... if self.check_if_answer_reached(): self.answer_reached = True if self.stream_prefix: for t in self.last_tokens: sys.stdout.write(t) sys.stdout.flush() return # ... if yes, then print tokens from now on if self.answer_reached: sys.stdout.write(token) sys.stdout.flush()