You can't replace the docstring of a class:

```
In [1]: class A(object):
   ...:     pass
   ...: 

In [2]: A.__doc__ = "Foo"
---------------------------------------------------------------------------
AttributeError                            Traceback (most recent call last)
<ipython-input-2-5c34c0540338> in <module>()
----> 1 A.__doc__ = "Foo"

AttributeError: attribute '__doc__' of 'type' objects is not writable
```

and you can't replace the `__init__` method of an extension type.