On Fri, June 6, 2008 3:37 pm, Andreas Kostyrka wrote: > On Friday 06 June 2008 18:19:23 you wrote: > >> On Thu, June 5, 2008 9:39 am, Andreas Kostyrka wrote: >> >>> On Thursday 05 June 2008 00:18:55 Marilyn Davis wrote: >>> >>>> You listed __init__ and I'm not sure I know what you mean. >>>> >>> >>> Well, __init__ can assign attributes to the instance that are >>> callable. >> >> Oh, well, Python is such a wide-open system. It keeps blowing my >> mind. > > Well, there is basically nothing that you cannot force the object system > of Python to do, almost. > > E.g. transplanting methods from class A to class B: > > > B.__dict__["method"] = A.__dict__["method"]
Oh dear. > > > Or deriving a class from itself (although a better name would be "from a > class that happened to be named the same). > > class A: pass class A(A): pass print A.__bases__ Oh dear. > > Now, as an observation, you will notice that most experienced Python > developers usually stay away from all this "magic" stuff. Rules of thumb > include "explicit is good, implicit is bad", and so on. Clearly stuff > tagged as "you really should know what you are doing". > >> >> I'm thinking that if you can provide an __init__ you can intercept >> methods the regular way, by providing them the regular way, and >> overriding them. > > Nope, I mentioned it, because this has been way back, when Python was > young and slow, this was a technique to speed up method lookup. > > Actually, it seems to work with py2.5 too, for oldstyle classes: > > > [EMAIL PROTECTED]:~/Videos$ python -m timeit -s 'class A:' -s ' def > m(self): pass' > 10000000 loops, best of 3: 0.0675 usec per loop > [EMAIL PROTECTED]:~/Videos$ python -m timeit -s 'class A:' -s ' def > m(self): pass' -s 'a=A()' 'a.m()' > 1000000 loops, best of 3: 0.747 usec per loop > [EMAIL PROTECTED]:~/Videos$ python -m timeit -s 'class A:' -s ' def > m(self): pass' -s 'a=A()' -s 'a.m=a.m' 'a.m()' > 1000000 loops, best of 3: 0.575 usec per loop Wow. > [EMAIL PROTECTED]:~/Videos$ python -m timeit -s 'class A(object):' -s ' > def m(self): pass' -s 'a=A()' 'a.m()' 1000000 loops, best of 3: 0.671 usec > per loop [EMAIL PROTECTED]:~/Videos$ python -m timeit -s 'class A(object):' > -s ' def m(self): pass' -s 'a=A()' -s 'a.m=a.m' 'a.m()' > 1000000 loops, best of 3: 0.641 usec per loop > > > The reason for this is, that the instance dictionary is the first place > that Python looks when looking for a.m. I see. Well, that is interesting. I'm glad I asked. > >> >> Thank you Andreas. This has been really interesting and instructive. >> > > Yeah, but please consider my comment. I think every developer should > have seen the possibilities, but in most cases forget about that ugly > stuff. You will get a headache, especially if you try to use the full > "power" that Python provides. One can usually be quite productive without > relying on these mechanisms. Yes, and if you consider the poor readers of your code, and/or if speed isn't so critical, it would be best to forget it. But, thank you for showing this to me. Do you have anything else really interesting to share? Marilyn Davis > > Andreas _______________________________________________ Tutor maillist - Tutor@python.org http://mail.python.org/mailman/listinfo/tutor
