langchain/document_loaders/gutenberg.py/GutenbergLoader/__init__
class GutenbergLoader:    def __init__(self, file_path: str):
        """Initialize with file path."""
        if not file_path.startswith("https://www.gutenberg.org"):
            raise ValueError("file path must start with 'https://www.gutenberg.org'")

        if not file_path.endswith(".txt"):
            raise ValueError("file path must end with '.txt'")

        self.file_path = file_path