ReActOutputParser Class — langchain Architecture

Architecture documentation for the ReActOutputParser class in output_parser.py from the langchain codebase.

Class python

Entity Profile

Dependency Diagram

graph TD
  040e163e_61b0_c9f4_7eff_dd7878f3f7fe["ReActOutputParser"]
  d9685a4b_26b0_bca9_f857_03bb2ffc9dd4["AgentOutputParser"]
  040e163e_61b0_c9f4_7eff_dd7878f3f7fe -->|extends| d9685a4b_26b0_bca9_f857_03bb2ffc9dd4
  1c037a99_fe6d_e353_78f4_508869dc6909["output_parser.py"]
  040e163e_61b0_c9f4_7eff_dd7878f3f7fe -->|defined in| 1c037a99_fe6d_e353_78f4_508869dc6909
  99c00fbe_ffee_45d9_c776_0e5e089bc1cc["parse()"]
  040e163e_61b0_c9f4_7eff_dd7878f3f7fe -->|method| 99c00fbe_ffee_45d9_c776_0e5e089bc1cc
  8b3f976c_a02c_4792_bd0b_53baeccfdefd["_type()"]
  040e163e_61b0_c9f4_7eff_dd7878f3f7fe -->|method| 8b3f976c_a02c_4792_bd0b_53baeccfdefd

Relationship Graph

Source Code

libs/langchain/langchain_classic/agents/react/output_parser.py lines 10–34

class ReActOutputParser(AgentOutputParser):
    """Output parser for the ReAct agent."""

    @override
    def parse(self, text: str) -> AgentAction | AgentFinish:
        action_prefix = "Action: "
        if not text.strip().split("\n")[-1].startswith(action_prefix):
            msg = f"Could not parse LLM Output: {text}"
            raise OutputParserException(msg)
        action_block = text.strip().split("\n")[-1]

        action_str = action_block[len(action_prefix) :]
        # Parse out the action and the directive.
        re_matches = re.search(r"(.*?)\[(.*?)\]", action_str)
        if re_matches is None:
            msg = f"Could not parse action directive: {action_str}"
            raise OutputParserException(msg)
        action, action_input = re_matches.group(1), re_matches.group(2)
        if action == "Finish":
            return AgentFinish({"output": action_input}, text)
        return AgentAction(action, action_input, text)

    @property
    def _type(self) -> str:
        return "react"