Before you are able to use an account_token you’ll need to either generate one here or obtain one by going through the OAuth flow. There are some examples at https://github.com/Dwolla/dwolla-v2-python#account-tokens that explain how to instantiate an account_token using either method. If you have any questions please let us know.
I took another look at the instantiate code and am using that to define the account_token using the access token and refresh token generated by the sandbox Apps page. Python is running into an error saying “name ‘client’ is not defined” . I thought client.Token would have been a function defined by the dwollav2 package.