<SYSTEM_TASK:>
Solve the following problem using Python, implementing the functions described below, one line at a time
<END_TASK>
<USER_TASK:>
Description:

def list_nodes():
    '''
    Return a list of registered VMs

    CLI Example:

    .. code-block:: bash

        salt '*' vboxmanage.list_nodes
    '''
    ret = {}
    nodes = list_nodes_full()
    for node in nodes:
        ret[node] = {
            'id': nodes[node]['UUID'],
            'image': nodes[node]['Guest OS'],
            'name': nodes[node]['Name'],
            'state': None,
            'private_ips': [],
            'public_ips': [],
        }
        ret[node]['size'] = '{0} RAM, {1} CPU'.format(
            nodes[node]['Memory size'],
            nodes[node]['Number of CPUs'],
        )
    return ret