BTCD client written with Go (golang) and less popular compared with other client such as Bitcoin Core, so i doubt there's python library specifically made for BTCD client.
However, it uses JSON-RPC and according to it's
documentation, it's fully compatible with the original bitcoind/bitcoin-qt (this statement might be partially wrong, since command on Bitcoin Core changed few times)
In theory, you can use Python library intended for Bitcoin Core JSON-RPC such as
https://github.com/jgarzik/python-bitcoinrpc
