Creating instances of untrusted new-style classes

[Michael Spencer]

Devan L wrote:
> Is there any safe way to create an instance of an untrusted class
> without consulting the class in any way? With old-style classes, I can
> recreate an instance from another one without worrying about malicious
> code (ignoring, for now, malicious code involving attribute access) as
> shown below.
> 
>>>> import types
>>>> class Foo:
> ...     def __init__(self, who, knows, what, args):
> ...         self.mystery_args = (who, knows, what, args)
> ...         print "Your code didn't expect the Spanish inquisition!"
> ...
>>>> f = Foo('spam','eggs','ham','bacon') # This would be in a restricted environment, though.
> Your code didn't expect the Spanish inquisition!
>>>> types.InstanceType(Foo, f.__dict__) # This wouldn't, but we never run that code, anyways.
> <__main__.Foo instance at 0x008B5FD0>
> 
> I'm not sure how to do the same for new-style classes, if it's at all
> possible to do from within Python. Is there any way to accomplish this,
> or is there no practical way to do so?
> 
> Thanks,
> - Devan
> 
 >>> class A(object):
...     def __init__(self, *args):
...         self.args = args
...         print "Calling __init__"
...
 >>> a = A("new","style")
Calling __init__
 >>> b = object.__new__(A)
 >>> b.__dict__ = a.__dict__.copy()
 >>> b.args
('new', 'style')
 >>> type(a) is type(b)
True
 >>>

HTH

Michael