Adding a list of descriptors to a class

[Bob B.]

I've been playing with descriptors lately.  I'm having one problem I
can't seem to find the answer to.  I want to assign a descriptor to a
list of attributes.  I know I should be able to add these somewhere in
the class's __dict__, but I can't figure out where.  Here's some code:

class MyDesc(object):
  def __init__(self, name=None, initVal=None):
    self.name = name
    self.value = initVal

  def __get__(self, obj, objtype):
    // Do some stuff
    self.value = "blah"
    return self.value

class MyClass(object):
  attributes = ('attr1', 'attr2')
  for attr in attributes:
    exec ("%s=MyDesc('%s')") % (attr, attr)

  // More stuff in the class

Ok, that "exec" is an ugly hack.  There's gotta be someway to plop
this straight into the class's __dict__ without doing that, but when I
try adding self.__class__.__dict__[attr] = MyDesc(attr) in MyClass's
__init__ method, I get the error: "TypeError: 'dictproxy' object does
not support item assignment"

Any ideas?

Thanks,
Bob