[pypy-issue] Issue #2325: `__slots__` and `__class__` assignment is broken (pypy/pypy)

[Daniel Holth]

New issue 2325: `__slots__` and `__class__` assignment is broken
https://bitbucket.org/pypy/pypy/issues/2325/__slots__-and-__class__-assignment-is

Daniel Holth:

SCons does a lot of `__class__` assignment with classes using `__slots__`. This doesn't work on PyPy. PyPy is documented to be limited here, but SCons is also careful to keep `__slots__` the same between morphing classes, while the error message suggests the class layout differs.

Small test case

```
#!python

class A(object):
    __slots__ = ['a']

class B(object):
    __slots__ = ['a']

a = A(); a.__class__ = B
```