[Python-Dev] About raising NotPortableWarning for CPython specific code

[Laura Creighton]

For those of you not at the Language Summit at PyCON the day before yesterday,
there was talk of identifying non-portable behaviour, such as relying on
CPython's reference counting garbage collector to close files for you as
soon as they become unreachable.  And then warning about them.

We have a real live user who has a large code base that relies on
the CPython behaviour that an object's __radd__ method will take precedence
over a list's inplace add behaviour.

The thread with the whole gory details begins here:
http://codespeak.net/pipermail/pypy-dev/2011q1/006958.html

My inclination is to declare code that relies on this as broken, rather
than patch every wretched container type in PyPy.  Can this become 
blessed as a 'you shouldn't have done this'?

Laura