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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 list_hbas(kwargs=None, call=None):
    '''
    List all HBAs for each host system; or all HBAs for a specified host
    system; or HBAs of specified type for each host system; or HBAs of
    specified type for a specified host system in this VMware environment

    .. note::

        You can specify type as either ``parallel``, ``iscsi``, ``block``
        or ``fibre``.

    To list all HBAs for each host system:

    CLI Example:

    .. code-block:: bash

        salt-cloud -f list_hbas my-vmware-config

    To list all HBAs for a specified host system:

    CLI Example:

    .. code-block:: bash

        salt-cloud -f list_hbas my-vmware-config host="hostSystemName"

    To list HBAs of specified type for each host system:

    CLI Example:

    .. code-block:: bash

        salt-cloud -f list_hbas my-vmware-config type="HBAType"

    To list HBAs of specified type for a specified host system:

    CLI Example:

    .. code-block:: bash

        salt-cloud -f list_hbas my-vmware-config host="hostSystemName" type="HBAtype"
    '''
    if call != 'function':
        raise SaltCloudSystemExit(
            'The list_hbas function must be called with '
            '-f or --function.'
        )

    ret = {}
    hba_type = kwargs.get('type').lower() if kwargs and 'type' in kwargs else None
    host_name = kwargs.get('host') if kwargs and 'host' in kwargs else None
    host_properties = [
        "name",
        "config.storageDevice.hostBusAdapter"
    ]

    if hba_type and hba_type not in ["parallel", "block", "iscsi", "fibre"]:
        raise SaltCloudSystemExit(
            'Specified hba type {0} currently not supported.'.format(hba_type)
        )

    host_list = salt.utils.vmware.get_mors_with_properties(_get_si(), vim.HostSystem, host_properties)

    for host in host_list:
        ret[host['name']] = {}
        for hba in host['config.storageDevice.hostBusAdapter']:
            hba_spec = {
                'driver': hba.driver,
                'status': hba.status,
                'type': type(hba).__name__.rsplit(".", 1)[1]
            }
            if hba_type:
                if isinstance(hba, _get_hba_type(hba_type)):
                    if hba.model in ret[host['name']]:
                        ret[host['name']][hba.model][hba.device] = hba_spec
                    else:
                        ret[host['name']][hba.model] = {hba.device: hba_spec}
            else:
                if hba.model in ret[host['name']]:
                    ret[host['name']][hba.model][hba.device] = hba_spec
                else:
                    ret[host['name']][hba.model] = {hba.device: hba_spec}
        if host['name'] == host_name:
            return {'HBAs by Host': {host_name: ret[host_name]}}

    return {'HBAs by Host': ret}