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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_datacenters(host, username, password, protocol=None, port=None):
    '''
    Returns a list of datacenters for the the specified host.

    host
        The location of the host.

    username
        The username used to login to the host, such as ``root``.

    password
        The password used to login to the host.

    protocol
        Optionally set to alternate protocol if the host is not using the default
        protocol. Default protocol is ``https``.

    port
        Optionally set to alternate port if the host is not using the default
        port. Default port is ``443``.

    CLI Example:

    .. code-block:: bash

        salt '*' vsphere.list_datacenters 1.2.3.4 root bad-password

    '''
    service_instance = salt.utils.vmware.get_service_instance(host=host,
                                                              username=username,
                                                              password=password,
                                                              protocol=protocol,
                                                              port=port)
    return salt.utils.vmware.list_datacenters(service_instance)