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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 _get_host_ref(service_instance, host, host_name=None):
    '''
    Helper function that returns a host object either from the host location or the host_name.
    If host_name is provided, that is the host_object that will be returned.

    The function will first search for hosts by DNS Name. If no hosts are found, it will
    try searching by IP Address.
    '''
    search_index = salt.utils.vmware.get_inventory(service_instance).searchIndex

    # First, try to find the host reference by DNS Name.
    if host_name:
        host_ref = search_index.FindByDnsName(dnsName=host_name, vmSearch=False)
    else:
        host_ref = search_index.FindByDnsName(dnsName=host, vmSearch=False)

    # If we couldn't find the host by DNS Name, then try the IP Address.
    if host_ref is None:
        host_ref = search_index.FindByIp(ip=host, vmSearch=False)

    return host_ref