'Look up a child atom.
\'names\' may be a list of atoms ([\'moov\', \'udta\']) or a string
specifying the complete path (\'moov.udta\').'

def __getitem__(self, names):

    if PY2:
        if isinstance(names, basestring):
            names = names.split('.')
    elif isinstance(names, bytes):
        names = names.split('.')
    for child in self.atoms:
        if (child.name == names[0]):
            return child[names[1:]]
    else:
        raise KeyError(('%r    not    found' % names[0]))
