Michael Tobis <[EMAIL PROTECTED]> wrote:
> I'd appreciate an explanation of why this doesn't work and any
> workarounds.
Special methods are looked up (for their automatic use) on the type, not
the instance. The workaround is therefore to set them on the type, too:
> class myint(object):
>
> def __init__(self,val):
> self.val = int(val)
> def mystr(self):
> return self.val.__str__()
> self.__str__ = new.instancemethod(mystr,self,mint) #doesn't
> work
What you need is to have *** as myint.__str__ *** the method you want to
get called. If you have a bunch of special methods that you want to
ensure delegate to self.val.(samemethod), you don't have to write them
out -- you can assign them as attributes of myint, with a simple loop of
setattr right after the class statement, or with a custom metaclass, or
whatever you find handiest.
For example (warning, untested code):
def _setdelegate(cls, delegate_cls, name):
method = getattr(delegate_cls, name)
def f(self, *a, **k): return method(self.val, *a, **k)
f.func_name = name
setattr(cls, name, f)
class myint(object):
def __init__(self, val):
self.val = int(val)
for spec in 'str repr hash hex oct'.split():
_setdelegate(myint, '__%s__' % spec)
This may be worth refactoring into a custom metaclass if you need more
than one class like this myint, but that's quite a side issue.
Alex
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