Using an OrderedDict for __dict__ in Python 3 using __prepare__

[Steven D'Aprano]

I'm using Python 3.1 and trying to create a class using an OrderedDict as
its __dict__, but it isn't working as I expect.

See http://www.python.org/dev/peps/pep-3115/ for further details.

Here is my code:


from collections import OrderedDict

# The metaclass
class OrderedClass(type):
# The prepare function
@classmethod
def __prepare__(metacls, name, bases): # No keywords in this case
print('calling metaclass __prepare__')
return OrderedDict()
# The metaclass invocation
def __new__(cls, name, bases, classdict):
print('calling metaclass __new__')
for x in cls, name, bases, classdict, type(classdict):
print(' ', x)
return type.__new__(cls, name, bases, classdict)

class MyClass(metaclass=OrderedClass):
spam = 'Cardinal Biggles'
ham = 'Ethel the Aardvark'
def method1(self):
pass
def method2(self):
pass

list(MyClass.__dict__.keys())


and the results I get:

calling metaclass __prepare__
calling metaclass __new__
<class '__main__.OrderedClass'>
MyClass
()
OrderedDict([('__module__', '__main__'), ('spam', 'Cardinal Biggles'),
('ham', 'Ethel the Aardvark'), ('method1', <function method1 at
0xb71a972c>), ('method2', <function method2 at 0xb71a96ac>)])
<class 'collections.OrderedDict'>

['__module__', 'method2', 'ham', 'spam', 'method1', '__dict__',
'__weakref__', '__doc__']


I expected that the output of MyClass.__dict__.keys would match the input
OrderedDict (ignoring the entries added later, like __module__ and
__doc__).

And I'm completely flummoxed by the existence of
MyClass.__dict__['__dict__'].


What am I doing wrong?