On  23-Oct-2006, at 16:58 , Larry Hastings wrote:

I genuinely don't know how many external Python extension modules are well-behaved in this regard.  But in case it helps: I just checked PIL, NumPy, PyWin32, and SWIG, and all of them were well-behaved.

Apart from stringobject.c, there was exactly one spot in the Python source tree which made assumptions about the structure of PyStringObjects (Mac/Modules/macos.c).  It's in the block starting with the comment "This is a hack:".  Note that this is unfixed in my patch, so just now all code using that self-avowed "hack" will break.

As the author of that hack, that gives me an idea for where you should look for code that will break: code that tries to expose low-level C interfaces to Python. (That hack replaced an even earlier worse hack, that took the id() of a string in Python and added a fixed number to it to get at the address of the string, to fill it into a structure, blush).

Look at packages such as win32, PyObjC, ctypes, bridges between Python and other languages, etc. That's where implementors are tempted to bend the rules of Official APIs for the benefit of serious optimizations. 
Jack Jansen, <Jack.Jansen@cwi.nl>, http://www.cwi.nl/~jack
If I can't dance I don't want to be part of your revolution -- Emma Goldman