I recently became aware that python-bitcoinlib is not a full bitcoin node implementation, but rather a set of tools to work with bitcoin-core cpp. I would like to know whether there are some fundamental issues with implementing a complete bitcoin node using python? Also if it were to be tried as a code-golf exercise (the shortest code to get the full node running) how many lines of code will it amount to in python ??
That strongly depends on your definition of complete. There are a number of implementations that implement parts of the Bitcoin node functionality. For example cdecker/pycoin has a solid network implementation, but does not include wallet management code and validation logic. richardkiss/pycoin on the other hand has some of the wallet logic, but lacks networking. Other libraries include:
But as far as I know there is no standalone client that includes a wallet as well as the networking code.
Check out Tinychain.
It isn't complete and will never inter-operate with the real Bitcoin network, but it is a "code golf" approach to implementing all the Bitcoin core ideas (validation, POW mining, peer-to-peer architecture, data structures like TxIn/TxOut/Block, etc) in Python.
There is a project, which is a complete bitcoin implementation in python. The source code at https://github.com/csunny/py-bitcoin