Having to use a ! for every system command is a dealbreaker for me. Honestly, it would be a dealbreaker even if you only had to do it once per line, but multiples is just too cumbersome to be a good replacement for bash.<p>If there were some way to put it in "shell mode", where you could avoid that, and perhaps use bang for "this line is now python", that might be okay.<p><i>EDIT</i>: I think I misunderstood what he was saying about multiple !'s. I still think ! is too cumbersome to use in front of commands by default, though. Also, when you use !, you don't have any way to test whether a call has run properly (i.e., no $? that I can figure out)