Change Default Shell to Python – Step-by-Step Guide

To get back into the system you can boot into single user mode by appending the number 1 at the end of the linux kernel line within GRUB. The method for doing this is roughly outlined in this U&L Q&A titled: Can I launch a process as root without launching root's login shell?.

Once you've done this you'll be dropped to a prompt as root from where you'll be able to reverse the changes you made to your shell. This will get your system back so that it's working correctly.

From here you'll likely want to run chsh for your username instead of whatever method you employed previously.