[Baypiggies] identity cache / flywheel design pattern

[Shannon -jj Behrens]

I'm have a program that intrinsically eats up a ton of memory.  I
often read lines from a file that are the same, so I end up with
multiple copies of the same data in memory.  I know that strings are
immutable, so there's no need for me to have two pointers to different
but equal data when I can have two pointers to the same data.  I
thought of a simple trick to fix this:

>>> s1 = "foo"
>>> s2 = ''.join(['f', 'o', 'o'])
>>> s1 == s2
True
>>> s1 is s2
False
>>> identity_cache = {}
>>> s1 = identity_cache.setdefault(s1, s1)
>>> s2 = identity_cache.setdefault(s2, s2)
>>> s1 == 'foo'
True
>>> s1 == s2
True
>>> s1 is s2
True

Of course, in a real library, I'd use lazy references.  Can anyone
comment on this trick?  Does it already exist in the library?  Is
there a standard name for this besides the flywheel design pattern?
Is that the correct name?  I might go looking to see if it's in the
Cookbook, but I'm not even sure if that's the right name.

Thanks,
-jj

-- 
Lisp programmers know the value of everything, but the cost of nothing...
On my Lisp, '() costs 4 bytes.
http://jjinux.blogspot.com/