def _form_types(form_type: str, allow_amended_filing: Optional[bool] = True):
    """
    Potentially expand to include amended filing, e.g.:
    "10-Q" -> "10-Q/A".
    """
    assert form_type in VALID_FILING_TYPES
    if allow_amended_filing and not form_type.endswith("/A"):
        return [form_type, f"{form_type}/A"]
    else:
        return [form_type]

    Potentially expand to include amended filing, e.g.:
    "10-Q" -> "10-Q/A".
    
llama-index-integrations/readers/llama-index-readers-sec-filings/llama_index/readers/sec_filings/prepline_sec_filings/fetch.py