Feature Requests item #1465406, was opened at 2006-04-05 23:30 Message generated for change (Comment added) made by ciw42 You can respond by visiting: https://sourceforge.net/tracker/?func=detail&atid=355470&aid=1465406&group_id=5470
Please note that this message will contain a full copy of the comment thread, including the initial issue submission, for this request, not just the latest update. Category: Parser/Compiler Group: None >Status: Open >Resolution: None Priority: 5 Submitted By: Chris Wilson (ciw42) Assigned to: Nobody/Anonymous (nobody) Summary: Allowing the definition of constants Initial Comment: One of the current optimizations due in v2.5 includes constant folding of expressions, which as it stands serves as a way of somply getting rid of a redundant arithmetic operations and the like. In practice, it's rare a developer would leave an expression such as "2+3" sat in his/her code, but by allowing the declaration of constants within a script, it could make this new feature *much* more useful. As an example, in a recent script I had the following at the top, outside the main loop: SCREEN_WIDTH=640 SCREEN_HEIGHT=480 SCREEN_RATIO=SCREEN_WIDTH/SCREEN_HEIGHT As SCREEN_RATIO is used a number of times during my main loop, it makes sense to pre-calculate it to avoid the extra processing, but if the compiler were aware that SCREEN_WIDTH and SCREEN_HEIGHT were constants, it could optimise out the calculation and I could include the calculation in-place. I frequently make use of "constants" to make my code more readable, and wonder whether there is any performance penalty or lack of optimisation going on due to them in fact being regular variables? ---------------------------------------------------------------------- >Comment By: Chris Wilson (ciw42) Date: 2006-04-06 21:59 Message: Logged In: YES user_id=1018283 I've re-opened this, as I don't feel it would be difficult to implement or require any fundamental changes to the parser or runtime. In fact, it would be very easy, and potentially very useful beyond the scope of my initial suggestion. Appologies to rhettinger if this seems rude, but I would ask that you give the following some consideration. The addition of a "const" or similar compiler directive would allow the compiler to simply do an on-the-fly substitution for the specified value/string etc. There would be no code analysis required, and adding this type of functionality would carry no real overheads or further complicate the compilation process. There would be no changes required within the runtime. Once substituted, the already incorporated compiler constant folding features would then come into play. I suppose, that what I'm suggesting is effectively a basic pre-compiler macro feature. This in itself may prove useful in many other situations. ---------------------------------------------------------------------- Comment By: Raymond Hettinger (rhettinger) Date: 2006-04-05 23:57 Message: Logged In: YES user_id=80475 Python is too dynamic for this kind of optimization to be done automatically. If those "constants" are defined at the module level, they can be changed by code outside the module. Even within the module, it would take a thorough analysis of the code to determine that nothing was trying to alter the value of the global variable. If the "constant" is defined inside a function, it is still a local variable subject to change by later lines in function. Your best bet is to use the bind_consts recipe at ASPN. It will automatically turn some global references into locals: http://aspn.activestate.com/ASPN/Cookbook/Python/Recipe/277 940 It may be possible to adapt the recipe to go an additional step and fold the globals "constants". ---------------------------------------------------------------------- You can respond by visiting: https://sourceforge.net/tracker/?func=detail&atid=355470&aid=1465406&group_id=5470 _______________________________________________ Python-bugs-list mailing list Unsubscribe: http://mail.python.org/mailman/options/python-bugs-list/archive%40mail-archive.com
