[EMAIL PROTECTED] <[EMAIL PROTECTED]> wrote: > why would binding to a function-local name speeds up performance?
Like any other constant-hoisting, pulling the lookup out of the loop speeds things up because otherwise Python must repeat the lookup each time through the loop (Python doesn't _know_ that, for example, zip.zap is always the same bound method object -- without potentially deep analysis, it can't rule out that looking up zap on zip has side effects and the like, so when you tell it to look it up, it looks it up, no ifs, no buts). You can measure the effect with -mtimeit ...: brain:~ alex$ python -mtimeit -s'def f(L): > for x in xrange(1000): L.append' 'f([])' 1000 loops, best of 3: 215 usec per loop brain:~ alex$ python -mtimeit -s'def g(L): > ap = L.append > for x in xrange(1000): ap' 'g([])' 10000 loops, best of 3: 79.1 usec per loop note that in each function f and g I'm doing only the lookup, not the call to the method thus looked up. Of course, this depends on the fact that for a function to use a local variable takes very little time indeed (since the compiler identifies which variables are local, and transforms any use of their names into a rapid indexing of a "local variables array", at the time the def statement executes -- so by the time the function gets called, i.e., that its body executes, that execution takes advantage of this optimization automatically performed by the Python compiler). Alex -- http://mail.python.org/mailman/listinfo/python-list
