I can't do the same with the PrivateKey: passing both .secret_exponential() or .serialize() objects as PrivateKey secret doesn't return the expected values (a privkey' wif match). What the PrivateKey class is expecting as 'secret' ? 
Code:
pyspv.keys.PrivateKey(secret_exp_as_long.to_bytes(32, "big"))
Right, the private key class takes an array of bytes (= the private key in big endian format).
Thanks for checking out pyspv, I haven't put much work into it since because its announcement went quite unnoticed
