For one, it removed the ability to do % formatting with bytes objects. When working with a wire protocol like ssh, you need to work with sequences of bytes, no

For one, it removed the ability to do % formatting with bytes objects. When working with a wire protocol like ssh, you need to work with sequences of bytes, not Unicode strings, and porting code that assembled them using % formatting was a huge pain; I tried and failed to port paramiko to python 3.