Sending transaction with Python + raw protocol
First, if you want to learn how to construct a raw transaction, you should really go to this question: Redeeming a raw transaction step by step example required

Second, the tx_in needs an outpoint_hash, which is the hash of the previous transaction you're spending from.

Third, you should never, ever encode your private key to any part of the transaction as you did in tx_in["script"]. That should stay on a secure device and you need that in order to generate the signature.

Fourth, tx_in["script"] should be the same script from the oupoint (hash, index). The specifics of the script language which is encoded in hex (76a914...88ac) are OP codes you should study (see link above).

Fifth, this library does the signing elsewhere as script_bytes needs to be the actual public key and signature.

I think you'd find it easier to understand using a slightly more standard python library like pycoin (https://github.com/richardkiss/pycoin) or pybitcoin (https://github.com/blockstack/pybitcoin)