Pi bridge is to communicate with Pi with any customized front end/client program (written in any programming language) as connectivity works with TCP/IP sockets.
with python you can use TCP communication Libraries for connectivity with Pi bridge. the sample programs in python is available in complete socket documentation in Q. you can login to q.zerodha.com/pi and can download it for reference. Pi bridge is also available as plugin to connect amibroker to pi ,
Kite Connect API is a set of REST-like APIs that expose many capabilities required to build a complete investment and trading platform. Execute orders in real time, manage user portfolio, stream live market data, the connectivity is with websockets, If you are familiar with Programming and want to build your own customized trading application KITE Connect will be best choice.
NOTE: You can do semi automated trading by using pi bridge or KITE Connect. For further details on this you can write email to [email protected].