On Tuesday 18 January 2005 12:33 pm, John Lenton wrote: > > consider this: > > 1 >>> class C: > 2 ... x = property(str) > 3 ... > 4 >>> c = C() > 5 >>> c.x > 6 '<__main__.C instance at 0x4008d92c>' > 7 >>> setattr(c, 'x', c.x) > 8 >>> c.x > 9 '<__main__.C instance at 0x4008d92c>' > 10 >>> C.x > 11 <property object at 0x4009a7ac> > 12 >>> c.x = 2 > 13 >>> > > in line 5 you see that the x property so defined works. In line 7 you > remove it, replacing it with the computed value of the property. Line > 9 shows that it worked, line 11 shows that it didn't break the class, > and line 13 (through the absence of an exception) shows that it no > longer is 'special' (as it shouldn't be).
It wasn't "special" before, either -- I tried this myself, because I wasn't familiar with properties yet, and I was trying to figure out what you meant by that. The catch is that I think you meant to type: > 1 >>> class C(object): (i.e. so that C is a "new-style" class). Then we get "special" behavior (which answers my first question): >>> class C(object): ... x = property(str) ... >>> C.x <property object at 0x401e8cd4> >>> c = C() >>> c.x '<__main__.C object at 0x401e984c>' >>> c.x = 2 Traceback (most recent call last): File "<stdin>", line 1, in ? AttributeError: can't set attribute >>> Unfortunately this seems to break your technique, too: >>> setattr(c, 'x', c.x) Traceback (most recent call last): File "<stdin>", line 1, in ? AttributeError: can't set attribute Too bad. I was kind of hoping it was just a typo. :-( Unless I'm missing something, anyway. Cheers, Terry -- -- Terry Hancock ( hancock at anansispaceworks.com ) Anansi Spaceworks http://www.anansispaceworks.com -- http://mail.python.org/mailman/listinfo/python-list
