self.parser = parser or BibtexparserWrapper()
        self.max_docs = max_docs
        self.max_content_chars = max_content_chars
        self.load_extra_metadata = load_extra_metadata
        self.file_regex = re.compile(file_pattern)
    def _load_entry(self, entry: Mapping[str, Any]) -> Optional[Document]:
        import fitz
        parent_dir = Path(self.file_path).parent
        # regex is useful for Zotero flavor bibtex files
        file_names = self.file_regex.findall(entry.get("file", ""))
        if not file_names:
            return None
        texts: List[str] = []
        for file_name in file_names:
            try:
                with fitz.open(parent_dir / file_name) as f:
                    texts.extend(page.get_text() for page in f)
            except FileNotFoundError as e:
                logger.debug(e)
        content = "\n".join(texts) or entry.get("abstract", "")
        if self.max_content_chars:
            content = content[: self.max_content_chars]
        metadata = self.parser.get_metadata(entry, load_extra=self.load_extra_metadata)
        return Document(
            page_content=content,
            metadata=metadata,
        )
[docs]    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`"
            )