2006/8/24, Brett Cannon <[EMAIL PROTECTED]>: > > > > On 8/23/06, K.S.Sreeram <[EMAIL PROTECTED]> wrote: > > Hi all, > > > > I noticed in Python/ceval.c that LOAD_GLOBAL uses a dictionary lookup, > > and was wondering if that can be optimized to a simple array lookup. > > > No, not as the language stands now. > > > If i'm right there are 3 kinds of name lookups: locals, outer > > scopes(closures), and globals. (not counting attribute lookup). Locals > > are identified by, either the presence of assignments, or their presence > > in the arg list. So all name lookups can be classified into the 3 types > > at compile/load time. > > > > Since we know, at load time, which names are global.. Can't we simply > > build a global name table and replace LOAD_GLOBALs with a lookup at the > > corresponding index into the global name table? > > > But we don't know statically what the globals will be. You can import a > module and put something in its global namespace externally. That is done > after load time or compile time. > I think that it can be implemented for the language as it stands now. I don't know whether it will be a good thing or not.
In principle, you can add a feature to dict implementation that will allow it to notify when the value of a specific key changes. If you have that, you can change LOAD_GLOBAL implementation to: 1. look for the global. 2. ask for notification when the global dict changes in a way that will change the meaning of the global. 3. change the LOAD_GLOBAL opcode to something like LOAD_CONST, and set the notification from the dict to update the LOAD_CONST opcode to the new object. In that way, LOAD_GLOBAL will cause a dict lookup only once. Changing the value of globals will require more work, though. Again, I'm not saying that it's desired, just that it's possible. Have a good day, Noam _______________________________________________ Python-Dev mailing list Python-Dev@python.org http://mail.python.org/mailman/listinfo/python-dev Unsubscribe: http://mail.python.org/mailman/options/python-dev/archive%40mail-archive.com
