Thanks for the report.

> Users should either be permitted to set debug on via an optional __init__ parameter,

This is already possible via the debug attribute (https://docs.python.org/3/library/shlex.html#shlex.shlex.debug), so I don't think adding a debug parameter to __init__ is necessary.

> or debug should be taken out of the initializer altogether.

+1. We can just remove the unreachable code.