On Dec 21, 12:40 pm, Jean-Paul Calderone <[EMAIL PROTECTED]> wrote: > On Fri, 21 Dec 2007 09:26:36 -0800 (PST), Mangabasi <[EMAIL PROTECTED]> wrote: > >Howdy, > > >I think it is easier to explain my question with a short example: > > >class Body: > > def __init__(self, pos): > > self.__dict__['pos'] = pos > > > def __setattr__(self, name, value): > > if name == 'pos': > > print 'pos changed to', value > > > self.__dict__[name] = value > > >>>> b = Body([0, 0]) > >>>> b.pos = [3, 4] > >>>> pos changed to [3, 4] > >>>> b.pos[0] = 5 # How do I detect this in the Body? > > >I would like to print 'pos changed to [5, 4]' when pos is modified > >with direct access to the pos object (i.e. b.pos[0] = 5) > > >My first instinct is to modify the Body's __dict__ by using > >metaclasses. > >I don't have any experience with meta classes but from what I remember > >this should be possible but I thought there could be a simpler way to > >do this. > > >What is the Pythonic way to do this? Can anybody provide a short > >example for either case (with or without metaclasses). > > You don't need metaclasses. You do need a wrapper around the list > so that you can intercept calls to __setitem__ (and whatever else) > which are made onto it. > > You might also consider making Body new-style (subclass object) and > using a property instead of a __setattr__ implementation. You still > need a wrapper, but the implementation of the rest of the feature > should be simpler. > > Jean-Paul- Hide quoted text - > > - Show quoted text -
Hi Jean-Paul, Sorry, I should have spelled this out in my post but I did not. For several reasons I do not wish to couple the pos object with the Body instances. In my case, I did not want pos objects (in my example they were lists but they can be other objects as well) to care about their parents. So the question is: How do we detect this in the Body? -- http://mail.python.org/mailman/listinfo/python-list
