Source code for langchain.prompts.example_selector.length_based
"""Select examples based on length."""
import re
from typing import Callable, Dict, List
from langchain.prompts.example_selector.base import BaseExampleSelector
from langchain.prompts.prompt import PromptTemplate
from langchain.pydantic_v1 import BaseModel, validator
def _get_length_based(text: str) -> int:
    return len(re.split("\n| ", text))
[docs]class LengthBasedExampleSelector(BaseExampleSelector, BaseModel):
    """Select examples based on length."""
    examples: List[dict]
    """A list of the examples that the prompt template expects."""
    example_prompt: PromptTemplate
    """Prompt template used to format the examples."""
    get_text_length: Callable[[str], int] = _get_length_based
    """Function to measure prompt length. Defaults to word count."""
    max_length: int = 2048
    """Max length for the prompt, beyond which examples are cut."""
    example_text_lengths: List[int] = []  #: :meta private:
[docs]    def add_example(self, example: Dict[str, str]) -> None:
        """Add new example to list."""
        self.examples.append(example)
        string_example = self.example_prompt.format(**example)
        self.example_text_lengths.append(self.get_text_length(string_example))
    @validator("example_text_lengths", always=True)
    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"]