If all we're doing is setting a dict to this with defaults of None, something like this would probably be easier to read and document:

```python
def __init__(self, details):
    details_fields = 'username', 'userid', 'password', 'password_verify', 'email', 'user_group_select'
    # set defaults
    self.details = {k: None for k in details_fields}
    # override with passed-in values
    self.details.update(details)
    # Handle password verify for the user if they didn't specify it in details
    if 'password_verify' not in details:
        self.details['password_verify'] = self.details['password']
```