Braintree no longer offers Transparent Redirect. Supported methods that helps with PCI compliance now are called "Drop-in" and "Hosted Fields"
An example of using the Drop-in interface with a Python backend server can be found on braintree's GitHub here.

At this time Braintree support is completely broken, but it seems to me that supporting the new methods should be much simpler than it was before (but I do not have the expertise needed to figure out how to update the existing code, sorry).