langchain/prompts/example_selector/length_based.py/LengthBasedExampleSelector/calculate_example_text_lengths
class LengthBasedExampleSelector:    def calculate_example_text_lengths(cls, v: List[int], values: Dict) -> List[int]:
        """Calculate text lengths if they don't exist."""
        # Check if text lengths were passed in
        if v:
            return v
        # If they were not, calculate them
        example_prompt = values["example_prompt"]
        get_text_length = values["get_text_length"]
        string_examples = [example_prompt.format(**eg) for eg in values["examples"]]
        return [get_text_length(eg) for eg in string_examples]