concat all inputs as object. DatetimeIndex, TimedeltaIndex and
    PeriodIndex are converted to object dtype before concatenation

def _concat_index_asobject(to_concat, name=None):
    """
    concat all inputs as object. DatetimeIndex, TimedeltaIndex and
    PeriodIndex are converted to object dtype before concatenation
    """
    from pandas import Index
    from pandas.core.arrays import ExtensionArray

    klasses = (ABCDatetimeIndex, ABCTimedeltaIndex, ABCPeriodIndex,
               ExtensionArray)
    to_concat = [x.astype(object) if isinstance(x, klasses) else x
                 for x in to_concat]

    self = to_concat[0]
    attribs = self._get_attributes_dict()
    attribs['name'] = name

    to_concat = [x._values if isinstance(x, Index) else x
                 for x in to_concat]

    return self._shallow_copy_with_infer(np.concatenate(to_concat), **attribs)