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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 source_absent(name):
    '''
    Ensure an image source is absent on the computenode

    name : string
        source url
    '''
    ret = {'name': name,
           'changes': {},
           'result': None,
           'comment': ''}

    if name not in __salt__['imgadm.sources']():
        # source is absent
        ret['result'] = True
        ret['comment'] = 'image source {0} is absent'.format(name)
    else:
        # remove source
        if __opts__['test']:
            res = {}
            ret['result'] = True
        else:
            res = __salt__['imgadm.source_delete'](name)
            ret['result'] = (name not in res)

        if ret['result']:
            ret['comment'] = 'image source {0} deleted'.format(name)
            ret['changes'][name] = 'deleted'
        else:
            ret['comment'] = 'image source {0} not deleted'.format(name)
            if 'Error' in res:
                ret['comment'] = '{0}: {1}'.format(ret['comment'], res['Error'])

    return ret