def unpack_header_kw(hdus, keywords, try_first=0):
    """ Looks up keyword values in FITS headers. Iterates over
    extensions until keyword is found, else returns False

    Can look up single keyword or several at once

    hdus - HDUList, exposure headers
    keywords - string or list, keywords to look up
    try_first - header index to look up first

    returns
    ----
    vals - single parameter value or list of parameter values
    """
    vals = []
    kws = [keywords] if not isinstance(keywords, list) else keywords
    for kw in kws:
        for hdu_ind in set([try_first, *range(len(hdus))]):
            try:
                hdu = hdus[hdu_ind]
                vals.append(hdu.header[kw])
                break
            except (IndexError, KeyError):
                pass
        else:
            vals.append(False)
    if not isinstance(keywords, list):
        return vals[0]
    return vals
