Is there a simple python script for xpub generation from private key
Yes, I'd say the simplest way is to use python bip39 implementation of trezor, this one file should be enough with methods:
to_seed - to convert list of the words into seed and
to_hd_master_key - to generate master xpub/xpriv
It doesn't support further derivations (which require a bit more dependencies), for which I'd suggest using bip32 library.