def safeget(dct, *keys):
    """
    retrieves the specified value from the specified keys of a dictionary
    Args:
        dct (dict) : a dictionary containing pubmed metadata
        *keys : path of keys
    Returns:
        dct: desired value from dictionairy
    """
    for key in keys:
        try:
            dct = dct[key]
        except KeyError:
            return None
    return dct