get_template_variables() — langchain Function Reference

Architecture documentation for the get_template_variables() function in string.py from the langchain codebase.

Function python PromptManagement ExampleSelection calls 3 called by 1

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PromptManagement→ ExampleSelection→ get_template_variables() — langchain Function Reference

Dependency Diagram

graph TD
  f102027d_2a56_058a_1cf8_8ec4c6f8a103["get_template_variables()"]
  a7a9f16f_a913_8e85_a792_d083dd92c428["string.py"]
  f102027d_2a56_058a_1cf8_8ec4c6f8a103 -->|defined in| a7a9f16f_a913_8e85_a792_d083dd92c428
  f102027d_2a56_058a_1cf8_8ec4c6f8a103["get_template_variables()"]
  f102027d_2a56_058a_1cf8_8ec4c6f8a103 -->|calls| f102027d_2a56_058a_1cf8_8ec4c6f8a103
  f102027d_2a56_058a_1cf8_8ec4c6f8a103["get_template_variables()"]
  f102027d_2a56_058a_1cf8_8ec4c6f8a103 -->|calls| f102027d_2a56_058a_1cf8_8ec4c6f8a103
  f53efb83_eef2_e36c_1360_c5fe4961e401["_get_jinja2_variables_from_template()"]
  f102027d_2a56_058a_1cf8_8ec4c6f8a103 -->|calls| f53efb83_eef2_e36c_1360_c5fe4961e401
  8a2cca12_2ece_1825_717e_3fd839530d4d["mustache_template_vars()"]
  f102027d_2a56_058a_1cf8_8ec4c6f8a103 -->|calls| 8a2cca12_2ece_1825_717e_3fd839530d4d
  style f102027d_2a56_058a_1cf8_8ec4c6f8a103 fill:#6366f1,stroke:#818cf8,color:#fff

Relationship Graph

Source Code

libs/core/langchain_core/prompts/string.py lines 254–306

def get_template_variables(template: str, template_format: str) -> list[str]:
    """Get the variables from the template.

    Args:
        template: The template string.
        template_format: The template format.

            Should be one of `'f-string'`, `'mustache'` or `'jinja2'`.

    Returns:
        The variables from the template.

    Raises:
        ValueError: If the template format is not supported.
    """
    if template_format == "jinja2":
        # Get the variables for the template
        input_variables = _get_jinja2_variables_from_template(template)
    elif template_format == "f-string":
        input_variables = {
            v for _, v, _, _ in Formatter().parse(template) if v is not None
        }
    elif template_format == "mustache":
        input_variables = mustache_template_vars(template)
    else:
        msg = f"Unsupported template format: {template_format}"
        raise ValueError(msg)

    # For f-strings, block attribute access and indexing syntax
    # This prevents template injection attacks via accessing dangerous attributes
    if template_format == "f-string":
        for var in input_variables:
            # Formatter().parse() returns field names with dots/brackets if present
            # e.g., "obj.attr" or "obj[0]" - we need to block these
            if "." in var or "[" in var or "]" in var:
                msg = (
                    f"Invalid variable name {var!r} in f-string template. "
                    f"Variable names cannot contain attribute "
                    f"access (.) or indexing ([])."
                )
                raise ValueError(msg)

            # Block variable names that are all digits (e.g., "0", "100")
            # These are interpreted as positional arguments, not keyword arguments
            if var.isdigit():
                msg = (
                    f"Invalid variable name {var!r} in f-string template. "
                    f"Variable names cannot be all digits as they are interpreted "
                    f"as positional arguments."
                )
                raise ValueError(msg)

    return sorted(input_variables)