12 confirmations; however, exchanges and entities handling very large amounts of Ether frequently are still encouraged to run two different Ethereum implementations and only accept transactions that have been confirmed by both for maximum security (e.g. Go & C++).
As the reference, the confirmations time is about 3 minutes.
However i can't find the corresponding source code in pyethereum project. Can anyone point out the position of the confirmation part ? Thanks a lot