from datetime import datetime


def is_sierra_export(file_handle: str) -> bool:
    """
    Returns only file handles that follow Sierra export naming schema

    Args:
        file_handle:            file handle

    Returns:
        boolean
    """

    if not isinstance(file_handle, str):
        return False

    if len(file_handle) != 25:
        return False

    if file_handle[:11] not in ("BookOpsQCb.", "BookOpsQCn."):
        return False

    try:
        datetime.strptime(file_handle[11:], "%Y%m%d%H%S%f")
    except ValueError:
        return False

    return True