First you need a system account. This takes 10 working days. You'll receive part of it via email and will need to call the DeX Helpdesk to get the rest of it.

https://dex.dss.gov.au/dex-user-access-request-form

I was first trying to use suds, and was able to authenticate however I kept getting 400 errors and never figured out why.

Install zeep: pip3 install zeep

This code should get you a listing of endpoints. Then print out some information about your user account and organisation:

#!/usr/bin/python3
from zeep import Client, Settings
from zeep.wsse.username import UsernameToken

settings = Settings(strict=False, raw_response=False, xml_huge_tree=True)
client = Client('https://api.dss.gov.au/datacollection/dex?wsdl',
                wsse=UsernameToken('<USERNAME>', '<PASSWORD>'), settings=settings)
result = client.service.GetUser()
print(dir(client.service))
print(result.body)

Output:

Forcing soap:address location to HTTPS
['AddCase', 'AddClient', 'AddOutlet', 'AddSession', 'DeleteCase', 'DeleteClient', 'DeleteOutlet',
'DeleteSession', 'GetAssessmentReferenceDetails', 'GetCase', 'GetClient', 'GetOrganisation', 
'GetOrganisationActivities', 'GetOutlet', 'GetOutletActivities', 'GetReferenceData', 'GetSession', 
'GetUser', 'Ping', 'SearchCase', 'SearchClient', 'UpdateCase', 'UpdateClient', 
'UpdateClientAssessments',  'UpdateOutlet', 'UpdateSession', 'UpdateSessionAssessments', 
'ValidateForDuplicateClient', '__class__', '__delattr__', '__dir__', '__doc__', '__eq__', '__format__',
'__ge__', '__get__', '__getattribute__', '__gt__', '__hash__', '__init__', '__init_subclass__',
'__le__', '__lt__', '__ne__', '__new__', '__reduce__', '__reduce_ex__', '__repr__', '__self__', 
'__self_class__', '__setattr__', '__sizeof__', '__str__', '__subclasshook__', '__thisclass__']

{
    'TransactionStatus': {
        'TransactionStatusCode': 'Success',
        'Messages': None
    },
    'User': {
        'UserName': 
        
...

If you need to see the raw XML, set raw_response=True and look at result.content.

Here's an example of sending string data with a request:

result = client.service.GetReferenceData(ReferenceDataCode="Gender")

Now, lets get some real data. This fetches a list of up to 10,000 Clients, sorted by ClientID.

PageSize, PageIndex, IsAscending and SortColumn are mandatory.

criteria = {'PageSize': 10000, 'PageIndex': 1,
            'IsAscending': True, 'SortColumn': 'ClientId'}
result = client.service.SearchClient(Criteria=criteria)
print(result.body)

Here's some code to generate the SLK:

slk = ''
family_name_alpha = ''.join(c for c in person.FamilyName if c.isalpha())
for i in 1, 2, 4:
    try:
        slk += family_name_alpha[i]
    except IndexError:
        slk += '2'
given_name_alpha = ''.join(c for c in person.GivenName if c.isalpha())
for i in 1, 2:
    try:
        slk += given_name_alpha[i]
    except IndexError:
        slk += '2'
slk += person.BirthDate.strftime("%d%m%Y")
gender_map = {'MALE': '1', 'FEMALE': '2', 'INTERSEX': '3', 'NOTSTATED': '9'}
slk += gender_map[person.GenderCode.DexCode]
slk = slk.upper()