def get_creator_data(h5group):
    """Read back creator data as written by ``stamp_creator_data``, returning a dictionary with
    keys as described for ``stamp_creator_data``. Missing fields are denoted with None. 
    The ``creation_time`` field is returned as a string."""
    attrs = h5group.attrs
    d = dict()
    for attr in ['creation_program', 'creation_user', 'creation_hostname',
        'creation_unix_time', 'creation_time']:
        d[attr] = attrs.get(attr)
    return d
