langchain/agents/react/base.py/DocstoreExplorer/__init__
class DocstoreExplorer:    def __init__(self, docstore: Docstore):
        """Initialize with a docstore, and set initial document to None."""
        self.docstore = docstore
        self.document: Optional[Document] = None
        self.lookup_str = ""
        self.lookup_index = 0