Is it possible to deploy a python script as a dApp on the Ethereum or NEO virtual network?
First of all: I don't know anything about NEO, I can just give you what I know about Ethereum.
As far as I know it is not possible to deploy a python script in the Ethereum network. In Ethereum you can only deploy Ethereum bytecode. It is compiled from smart contracts written in Solidity, Serpent, LLL or Vyper.
Other code than Ethereum bytecode will never be stored on the Ethereum blockchain (at least not in an executable way).
When you want to build a dApp you need to write the needed smart contract and (if necessary) somewhere host your python (or whatever) frontend and/or backend.