I have 2 small patches that I think should go to emacs-26, and I'm not
sure if they deserve their own individual reports. Is this alright, or
should I split them up in the future?

Anyway, these alleviate/solve some issues that I've seen people report.
The first patch provides more information to an error message, and the
second deals with pressing backspace in a python-mode buffer with an
active region.

When in a python-mode buffer with the contents:

def foo():
    print('bar')

with an active region and point at the "p", then pressing backspace
de-indents the line instead of deleting it. This is at odds with the
behaviour in other modes, where a similar action deletes the line, at
least with ‘delete-active-region’ non-nil.

I thought about making this behaviour conditional using
‘delete-active-region’, but that might be a bit inconsistent.