def modify_hosts(HostIds=None, AutoPlacement=None):
    """
    Modify the auto-placement setting of a Dedicated Host. When auto-placement is enabled, AWS will place instances that you launch with a tenancy of host , but without targeting a specific host ID, onto any available Dedicated Host in your account which has auto-placement enabled. When auto-placement is disabled, you need to provide a host ID if you want the instance to launch onto a specific host. If no host ID is provided, the instance will be launched onto a suitable host which has auto-placement enabled.
    See also: AWS API Documentation
    
    
    :example: response = client.modify_hosts(
        HostIds=[
            'string',
        ],
        AutoPlacement='on'|'off'
    )
    
    
    :type HostIds: list
    :param HostIds: [REQUIRED]
            The host IDs of the Dedicated Hosts you want to modify.
            (string) --
            

    :type AutoPlacement: string
    :param AutoPlacement: [REQUIRED]
            Specify whether to enable or disable auto-placement.
            

    :rtype: dict
    :return: {
        'Successful': [
            'string',
        ],
        'Unsuccessful': [
            {
                'ResourceId': 'string',
                'Error': {
                    'Code': 'string',
                    'Message': 'string'
                }
            },
        ]
    }
    
    
    :returns: 
    (string) --
    
    """
    pass
