== Another introspection trick

Here's another example of Python's introspection and command
interpreter being useful:

> _[x for x in dir(m) if isinstance(getattr(m, x), str) and 'localhost' in getattr(m, x)]_

One of our Mailman lists had been accidentally set up thinking that
the machine's name was 'localhost', instead of the machine's actual
hostname, and this was causing problems. Mailman is written in Python
and offers access to the internals of list data via an interactive
Python interpreter (through the _withlist_ program). This one-off bit of
introspection was basically a grep over all the lists's attributes.

I won't claim that this would be good style in a program, but as
something I typed at the Python interpreter's command line it was very
handy. In this, it's like shells and shell scripts; we do things on the
command line that we'd never do in shell scripts.

(The _isinstance()_ check is necessary to keep the next clause from
potentially throwing an exception on non-string attributes, which would
abort the entire list comprehension.)