En Thu, 03 Apr 2008 21:57:56 -0300, Brian Vanderburg II <[EMAIL PROTECTED]> escribió:
> I don't know if this is the correct place to send this question. > > I've checked out some ways to get this to work. I want to be able to > add a new function to an instance of an object. I've tested two > different methods that cause problems with 'deleting'/garbage collection > (__del__ may never get called), but implemented one sort of hackishly > maybe that works find. I'm wondering if there is more of an official way > than mine. > > 1. > import new > import gc > > class A: > def __del__(x): > print "Deleting" > > def f(x): > print x > > a = A() > a.f = new.instancemethod(a,f) > a.f() # This works > del a # Not what is expected > gc.collect() # Works, but __del__ does not get called O thou of little faith, wherefore didst thou doubt? This is the simplest and preferred way, and it works! It's true that there is a reference cycle between a and a.f, but the garbage collector is able to detect it and dispose of those objects *UNLESS* any of them contains a __del__ method written in Python. See http://docs.python.org/ref/customization.html So this *is* the right way, and the object `a` would have been deleted if you had not tried to witness the deletion itself... You perturbed the system in a non trivial way just by attempting to observe it - isn't this Quantum Mechanics applied to Python programming? We need a side-effect triggered by __del__ but written in C... hmmm, what about flushing a file buffer? py> import new py> import gc py> import os py> py> class myfile(file): # just to be able to add attributes ... pass ... py> def f(x): ... print x ... py> a = myfile("a.aaa","w") py> print os.stat("a.aaa").st_size # 0 0 py> a.f = new.instancemethod(f, a) py> a.f() # This works <open file 'a.aaa', mode 'w' at 0x00A293F8> py> a.write("X") # a single char, should stay on write buffer py> print os.stat("a.aaa").st_size # still 0 0 py> del a py> print os.stat("a.aaa").st_size # still 0 0 py> gc.collect() 3 py> print os.stat("a.aaa").st_size # now 1 1 -- Gabriel Genellina -- http://mail.python.org/mailman/listinfo/python-list
