new-style class instance check

[Robert Brewer]

Richard Gruet wrote:
> Robert
> 
> Thank you for your suggestion.
> But unfortunately, isNewStyleClassInstance(o) must return False for
> *everything but* an instance of a new-style class. If o is 
> e.g. a function:
> def foo(): pass
> foo.__class__.rmo
> <built-in method mro of type object at 0x1E0BA9E0>
> 
> so isNewStyleClassInstance(foo) would return True !

Yes, function() is new-style. So is int. I think what you're asking for
is not whether a given object is new-style or not, but whether it is a
*user-defined* new-style object (correct me if I'm wrong). The problem
with that approach occurs with, e.g.:

class RangedInt(int):
    def __init__(self, value, lower, upper):
        int.__init__(self, value)
        self.lower = lower
        self.upper = upper

Now, since int() creates new-style objects, should RangedInt pass your
test or not? If not, then you could simply check the mro to see that
there are only two values: the target class and "object":

>>> class C(object): pass
... 
>>> C.mro()
[<class '__main__.C'>, <type 'object'>]

...but if you want RangedInt(3) to pass when int(3) doesn't, you've got
more inspection to do:

>>> RangedInt.mro()
[<class '__main__.RangedInt'>, <type 'int'>, <type 'object'>]


Robert Brewer
MIS
Amor Ministries
fumanchu at amor.org