langchain/document_loaders/bibtex.py/BibtexLoader/lazy_load
class BibtexLoader:    def lazy_load(self) -> Iterator[Document]:
        """Load bibtex file using bibtexparser and get the article texts plus the

        article metadata.

        See https://bibtexparser.readthedocs.io/en/master/

        Returns:
            a list of documents with the document.page_content in text format
        """
        try:
            import fitz  # noqa: F401
        except ImportError:
            raise ImportError(
                "PyMuPDF package not found, please install it with "
                "`pip install pymupdf`"
            )

        entries = self.parser.load_bibtex_entries(self.file_path)
        if self.max_docs:
            entries = entries[: self.max_docs]
        for entry in entries:
            doc = self._load_entry(entry)
            if doc:
                yield doc