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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 vdi_list(call=None, kwargs=None):
    '''
    Return available Xen VDI images

    If this function is called with the ``-f`` or ``--function`` then
    it can return a list with minimal deatil using the ``terse=True`` keyword
    argument.

    .. code-block:: bash

        salt-cloud -f vdi_list myxen terse=True

    '''
    if call == 'action':
        raise SaltCloudException(
            'This function must be called with -f or --function.')
    log.debug('kwargs is %s', kwargs)
    if kwargs is not None:
        if 'terse' in kwargs:
            if kwargs['terse'] == 'True':
                terse = True
            else:
                terse = False
        else:
            terse = False
    else:
        kwargs = {}
        terse = False
    session = _get_session()
    vdis = session.xenapi.VDI.get_all()
    ret = {}
    for vdi in vdis:
        data = session.xenapi.VDI.get_record(vdi)
        log.debug(type(terse))
        if terse is True:
            ret[data.get('name_label')] = {
                'uuid': data.get('uuid'),
                'OpqueRef': vdi}
        else:
            data.update({'OpaqueRef': vdi})
            ret[data.get('name_label')] = data
    return ret