langchain/output_parsers/pydantic.py/PydanticOutputParser/get_format_instructions
class PydanticOutputParser:    def get_format_instructions(self) -> str:
        schema = self.pydantic_object.schema()

        # Remove extraneous fields.
        reduced_schema = schema
        if "title" in reduced_schema:
            del reduced_schema["title"]
        if "type" in reduced_schema:
            del reduced_schema["type"]
        # Ensure json in context is well-formed with double quotes.
        schema_str = json.dumps(reduced_schema)

        return PYDANTIC_FORMAT_INSTRUCTIONS.format(schema=schema_str)