TextAccessor Class — langchain Architecture

Source Code

libs/core/langchain_core/messages/base.py lines 47–90

class TextAccessor(str):
    """String-like object that supports both property and method access patterns.

    Exists to maintain backward compatibility while transitioning from method-based to
    property-based text access in message objects. In LangChain <v1.0, message text was
    accessed via `.text()` method calls. In v1.0=<, the preferred pattern is property
    access via `.text`.

    Rather than breaking existing code immediately, `TextAccessor` allows both
    patterns:
    - Modern property access: `message.text` (returns string directly)
    - Legacy method access: `message.text()` (callable, emits deprecation warning)

    """

    __slots__ = ()

    def __new__(cls, value: str) -> Self:
        """Create new TextAccessor instance."""
        return str.__new__(cls, value)

    def __call__(self) -> str:
        """Enable method-style text access for backward compatibility.

        This method exists solely to support legacy code that calls `.text()`
        as a method. New code should use property access (`.text`) instead.

        !!! deprecated
            As of `langchain-core` 1.0.0, calling `.text()` as a method is deprecated.
            Use `.text` as a property instead. This method will be removed in 2.0.0.

        Returns:
            The string content, identical to property access.

        """
        warn_deprecated(
            since="1.0.0",
            message=(
                "Calling .text() as a method is deprecated. "
                "Use .text as a property instead (e.g., message.text)."
            ),
            removal="2.0.0",
        )
        return str(self)