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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_clusters_by_datacenter(kwargs=None, call=None):
    '''
    List clusters for each datacenter; or clusters for a specified datacenter in
    this VMware environment

    To list clusters for each datacenter:

    CLI Example:

    .. code-block:: bash

        salt-cloud -f list_clusters_by_datacenter my-vmware-config

    To list clusters for a specified datacenter:

    CLI Example:

    .. code-block:: bash

        salt-cloud -f list_clusters_by_datacenter my-vmware-config datacenter="datacenterName"
    '''
    if call != 'function':
        raise SaltCloudSystemExit(
            'The list_clusters_by_datacenter function must be called with '
            '-f or --function.'
        )

    ret = {}
    datacenter_name = kwargs.get('datacenter') if kwargs and 'datacenter' in kwargs else None
    datacenter_properties = ["name"]

    datacenter_list = salt.utils.vmware.get_mors_with_properties(_get_si(), vim.Datacenter, datacenter_properties)

    for datacenter in datacenter_list:
        ret[datacenter['name']] = []
        for cluster in datacenter['object'].hostFolder.childEntity:
            if isinstance(cluster, vim.ClusterComputeResource):
                ret[datacenter['name']].append(cluster.name)
        if datacenter_name and datacenter_name == datacenter['name']:
            return {'Clusters by Datacenter': {datacenter_name: ret[datacenter_name]}}

    return {'Clusters by Datacenter': ret}