You will get the same problem for common idiom of using a singleton for optional parameters without default value.

    _singleton = object()
    def get(key, default=_signleton):
        if default is _signleton:
            ...

And for other objects whos repr contains "at 0x...".

And even more complex problem with sets.

When test the pydoc output, ignore non-deterministic parts. For example, doctest allows you to use a placeholder.

   >>> C() #doctest: +ELLIPSIS
   <__main__.C instance at 0x...>