'If the configuration setting ``astropy.utils.iers.conf.auto_download``
is set to True (default), then open a recent version of the IERS-A
table with predictions for UT1-UTC and polar motion out to
approximately one year from now.  If the available version of this file
is older than ``astropy.utils.iers.conf.auto_max_age`` days old
(or non-existent) then it will be downloaded over the network and cached.
If the configuration setting ``astropy.utils.iers.conf.auto_download``
is set to False then ``astropy.utils.iers.IERS()`` is returned.  This
is normally the IERS-B table that is supplied with astropy.
On the first call in a session, the table will be memoized (in the
``iers_table`` class attribute), and further calls to ``open`` will
return this stored table.
Returns
`~astropy.table.QTable` instance with IERS (Earth rotation) data columns'

@classmethod
def open(cls):

    if (not conf.auto_download):
        cls.iers_table = IERS.open()
        return cls.iers_table
    if (cls.iers_table is not None):
        if (cls.iers_table.meta.get(u'data_url') == conf.iers_auto_url):
            return cls.iers_table
    try:
        filename = download_file(conf.iers_auto_url, cache=True)
    except Exception as err:
        warn(AstropyWarning(u'failed    to    download    {},    using    local    IERS-B:    {}'.format(conf.iers_auto_url, str(err))))
        cls.iers_table = IERS.open()
        return cls.iers_table
    cls.iers_table = cls.read(file=filename)
    cls.iers_table.meta[u'data_url'] = str(conf.iers_auto_url)
    return cls.iers_table
