== When I've interned Python strings

One day, I read the following [[on reddit's r/python
http://www.reddit.com/r/programming/comments/xgl0t/try_to_keep_those_python_strings_immutable/]]:

> Is manually interning a string every a good idea? I'm having trouble
> thinking of a use case where the cost is justified outside the
> compilation cycle.

and a reply:
> I've yet to run into a situation where it was, but I guess it could
> be in a very restricted number of situations, such as a small set of
> non-literal strings generated over and over again (e.g. some sort of
> parser), interning could reduce memory pressure.

This is exactly the case that I ran into at one point, with [[one of
my Python daemons DWikiGithub]] which was being used in [[a fairly
demanding situation IndustrialPython]] where I wanted to minimize the
memory usage and memory churn over time. My program had three important
features for having this make sense: it had big files to parse, there
was a lot of repeated text in the files (text that had to be saved),
and the files were changed a bit and reloaded on a relatively frequent
basis.

Interning repeated text is an obvious win for memory usage, if you have
a decent amount of it (measuring helps to know this). In my situation it
also helped avoid [[memory churn MinimizingObjectChurn]] during reloads
of the files. When you reload a configuration file, the usual case is
that almost all of the text is the same as it was the last time; this
creates a lot of text and string duplication as you re-parse the file
and get the same results as last time for most of it. Interning strings
here insures that you do not create a boatload of new strings every time
you reload the configuration file (and discard a boatload of old ones);
instead you're likely to create only a few new ones and discard a few
old ones.

Of course all of this care and interning may be a micro-optimization
that doesn't make any difference in your actual circumstance. Interning
strings is a performance optimization, so like any other optimization
you should measure it to see if it gives you any benefits.

(For my program in our specific situation, it was one of a number of
things that did make a visible difference.)