langchain/document_loaders/parsers/generic.py/MimeTypeBasedParser/__init__
class MimeTypeBasedParser:    def __init__(
        self,
        handlers: Mapping[str, BaseBlobParser],
        *,
        fallback_parser: Optional[BaseBlobParser] = None,
    ) -> None:
        """Define a parser that uses mime-types to determine how to parse a blob.

        Args:
            handlers: A mapping from mime-types to functions that take a blob, parse it
                      and return a document.
            fallback_parser: A fallback_parser parser to use if the mime-type is not
                             found in the handlers. If provided, this parser will be
                             used to parse blobs with all mime-types not found in
                             the handlers.
                             If not provided, a ValueError will be raised if the
                             mime-type is not found in the handlers.
        """
        self.handlers = handlers
        self.fallback_parser = fallback_parser