xml.py — langchain Source File

Source Code

import re
from typing import Literal

from langchain_core.agents import AgentAction, AgentFinish
from pydantic import Field
from typing_extensions import override

from langchain_classic.agents import AgentOutputParser


def _unescape(text: str) -> str:
    """Convert custom tag delimiters back into XML tags."""
    replacements = {
        "[[tool]]": "<tool>",
        "[[/tool]]": "</tool>",
        "[[tool_input]]": "<tool_input>",
        "[[/tool_input]]": "</tool_input>",
        "[[observation]]": "<observation>",
        "[[/observation]]": "</observation>",
    }
    for repl, orig in replacements.items():
        text = text.replace(repl, orig)
    return text


class XMLAgentOutputParser(AgentOutputParser):
    """Parses tool invocations and final answers from XML-formatted agent output.

    This parser extracts structured information from XML tags to determine whether
    an agent should perform a tool action or provide a final answer. It includes
    built-in escaping support to safely handle tool names and inputs
    containing XML special characters.

    Args:
        escape_format: The escaping format to use when parsing XML content.
            Supports 'minimal' which uses custom delimiters like [[tool]] to replace
            XML tags within content, preventing parsing conflicts.
            Use 'minimal' if using a corresponding encoding format that uses
            the _escape function when formatting the output (e.g., with format_xml).

    Expected formats:
        Tool invocation (returns AgentAction):
            <tool>search</tool>
            <tool_input>what is 2 + 2</tool_input>

        Final answer (returns AgentFinish):
            <final_answer>The answer is 4</final_answer>

    !!! note
        Minimal escaping allows tool names containing XML tags to be safely represented.
        For example, a tool named `search<tool>nested</tool>` would be escaped as
        `search[[tool]]nested[[/tool]]` in the XML and automatically unescaped during
        parsing.

    Raises:
        ValueError: If the input doesn't match either expected XML format or
            contains malformed XML structure.
    """

    escape_format: Literal["minimal"] | None = Field(default="minimal")
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