How to generate a signature and send a valid request in indy-vdr using Python?

Question

I want to send a ledger request in Hyperledger Indy using indy-vdr Python. To do that, I think I need to generate a signature.

My attempts to send a nym_request in Python without valid signatures result in errors like this:

indy_vdr.error.VdrError: Request failed: client request invalid: insufficient number of valid signatures

I read the Python demo for indy-vdr and they only have a placeholder signature b"sig" here: https://github.com/hyperledger/indy-vdr/blob/43aa575b6dab8e2f8a20af489dfc1bfccd7a832c/wrappers/python/demo/test.py#L97

In Rust, it looks like you can sign using private_key.sign here: https://github.com/hyperledger/indy-vdr/blob/43aa575b6dab8e2f8a20af489dfc1bfccd7a832c/libindy_vdr/tests/utils/crypto.rs#L35

What else can I do? Maybe I need to write my own Python function to call the Rust lib?