Neal Becker wrote: > I have a class (actually implemented in c++ using boost::python). For an > instance of this class, 'r', I'd like to support len (r). I don't want to > add it to the c++ code, because this is a unique situation: this class > should not normally support len(). > > So I try: > r = ring_int (10) > r.__len__ = lambda: 10 > > This doesn't work: >>>> len(r) > TypeError: object of type 'ring_int' has no len() > > It appears that __len__ is being looked up only on the class dict, not the > instance dict? What's the correct way to do this? (Of course, I could > just use inheritance, but this is an opportunity for me to learn more > about python)
Yes, they are only looked up on the class. Unfortunately, I don't find the paragraph in the language-ref that says so. BTW, could you stop setting the followup-to to a non-existing (at least for a standard newsreader) gmane-newsgroup? Diez -- http://mail.python.org/mailman/listinfo/python-list
