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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 host_list(call=None):
    '''
    Get a list of Xen Servers

    .. code-block:: bash

        salt-cloud -f host_list myxen
    '''
    if call == 'action':
        raise SaltCloudSystemExit(
            'This function must be called with -f, --function argument.'
        )
    ret = {}
    session = _get_session()
    hosts = session.xenapi.host.get_all()
    for host in hosts:
        host_record = session.xenapi.host.get_record(host)
        ret[host_record['name_label']] = host_record
    return ret