> I'm trying to solve a computational problem and of course speed and size is > important there. Apart from picking the right algorithm, I came across an > idea that could help speed up things and keep memory requirements down. What > I have is regions described by min and max coordinates. At first, I just > modeled these as a simple class containing two values for each axis. > > In a second step, I derived this class from tuple instead of object. Some > code then moved from __init__ to __new__ and some code that modified these > objects had to be changed to replace them instead. The upside to this is > that they can be used as keys in sets and dicts, which isn't the case for > mutable types[1]. > > What I'm now considering is to only allow a single instance of these objects > for each set of values, similar to interned strings. What I would gain is > that I could safely compare objects for identity instead of equality. What > I'm not yet sure is how much overhead that would give me and/or how to keep > it low. The idea is to store each instance in a set and after creating a new > object I would first look up an equal object in the global set and return > that instead, otherwise add the new one. > > The problem I foresee is that if I define equality as identity, this lookup > when creating will never eliminate duplicates. If I only fall back to > equality comparison for non-identical objects, I would probably sacrifice > most of the gain. If I build a dict mapping between the values and the > actual objects, I would have doubled the required memory and uselessly store > the same values twice there. > > Am I looking in the wrong direction? Is there some better approach? Please > don't tell me to use C, as I'm specifically interested in learning Python, > I'm pretty sure I could have solved the problem quickly in C++ otherwise. > Other suggestions? > > Cheers! > > Uli > > > [1] Somebody correct me if I'm wrong, but I believe I could have defined a > hashing function for the type and thus allowed its use in a set or dict, > right? However, goofing up because you accidentally modified an object and > changed its hash value is something I don't want to risk anyway.
I believe what you are looking for is (some variant of) the singleton pattern: http://en.wikipedia.org/wiki/Singleton_pattern How it's done in python see http://www.google.com/search?q=python+singleton Cheers, Daniel -- Psss, psss, put it down! - http://www.cafepress.com/putitdown -- http://mail.python.org/mailman/listinfo/python-list
