Not sure how I got it, but I ended up with an empty .cqlsh_history file. In that state, when starting cqlsh, you end up with:
Traceback (most recent call last):
File "bin/cqlsh", line 2588, in <module>
File "bin/cqlsh", line 2543, in main
IOError: [Errno 22] Invalid argument
Its a simple fix to check for a non-empty history file. I'll attach the patch.