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Solve the following problem using Python, implementing the functions described below, one line at a time
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Description:

def _expand_disk(disk):
    '''
    Convert the libcloud Volume object into something more serializable.
    '''
    ret = {}
    ret.update(disk.__dict__)
    zone = ret['extra']['zone']
    ret['extra']['zone'] = {}
    ret['extra']['zone'].update(zone.__dict__)
    return ret