According to Andrew Kuchling's and Moshe Zadka's "Python 2.0 what's new list", isinstance() and issubclass() already works on ExtensionClass-based stuff in Python 1.6. See http://starship.python.net/crew/amk/python/writing/new-python/new-python .html#SECTION000900000000000000000 That said, as for right now, I'm not sure if your extended functions do the right thing. Maybe someone else can comment.

-----Original Message----- From: Greg Ward [mailto:gward@mems-exchange.org] Sent: Wednesday, July 05, 2000 2:40 PM To: zope-dev@zope.org Subject: [Zope-dev] 'issubclass' and 'isinstance' on ExtensionClasses

Hi all --

surely I'm not the first to deal with this: I use 'isinstance()' a lot, and 'issubclass()' occasionally, for run-time type-checking. This breaks when using ZODB Persistent classes, or any other type of ExtensionClass for that matter.

I see no use of 'issubclass()' in the Zope lib/python directory, and only a few scattered uses of 'isinstance()'. (Checked both 2.1.5 and 2.2b2.) So maybe I *am* the first to worry about this. I'm surprised that ExtensionClass doesn't include enhanced versions of 'issubclass()' and 'isinstance()', though.

So, here are my versions. Critiques welcome. In particular, is "type(X) is not ClassType and hasattr(X, '__bases__')" an adequate determination that X is indeed an extension class?

If you folks want to include these with ExtensionClass (possibly with the leading "ec_" trimmed from the names), be my guest.

--snip snip------------------------------------------------------------- def ec_issubclass (class1, class2): """A version of 'issubclass' that works with extension classes as well as regular Python classes. """

# Both class objects are regular Python classes, so use the # built-in 'issubclass()'. if type(class1) is ClassType and type(class2) is ClassType: return __builtin__.issubclass(class1, class2)

# Both so-called class objects have a '__bases__' attribute: ie., # they aren't regular Python classes, but they sure look like them. # Assume they are extension classes and reimplement what the builtin # 'issubclass()' does behind the scenes. elif hasattr(class1, '__bases__') and hasattr(class2, '__bases__'): # XXX it appears that "ec.__class__ is type(ec)" for an # extension class 'ec': could we/should we use this as an # additional check for extension classes?

# Breadth-first traversal of class1's superclass tree. Order # doesn't matter because we're just looking for a "yes/no" # answer from the tree; if we were trying to resolve a name, # order would be important! stack = [class1] while stack: if stack[0] is class2: return 1 stack.extend(list(stack[0].__bases__)) del stack[0] else: return 0

# Not a regular class, not an extension class: blow up for consistency # with builtin 'issubclass()" else: raise TypeError, "arguments must be class or ExtensionClass objects"

# ec_issubclass ()

def ec_isinstance (object, klass): """A version of 'isinstance' that works with extension classes as well as regular Python classes."""

if type(klass) is ClassType: return isinstance(object, klass) elif hasattr(object, '__class__'): return ec_issubclass(object.__class__, klass) else: return 0

# ec_isinstance () --snip snip-------------------------------------------------------------

-- Greg Ward - software developer gward@mems-exchange.org MEMS Exchange / CNRI voice: +1-703-262-5376 Reston, Virginia, USA fax: +1-703-262-5367

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