On systems (Linux, OS X) where sizeof(wchar_t) is 4 and wchar_t arrays are 
usually encoded as UTF-32, it looks as though PyUnicode_FromWideChar 
simply truncates the 32-bit characters to 16-bits, thus giving incorrect 
results for characters outside the BMP.  I expected it to convert the UTF-
32 encoding to UTF-16.

Note that PyUnicode_FromWideChar is used to process command-line 
arguments, so strange things can happen when passing filenames with non-
BMP characters to a Python script.

Here's an OS X 10.5 Terminal session (current directory is the root of the 
py3k tree).

dickinsm$ cat test𐅭.py
from sys import argv
print("My arguments are: ",argv)
dickinsm$ ./python.exe test𐅭.py
My arguments are:  ['testŭ.py']
dickinsm$ ./python.exe Lib/tabnanny.py test𐅭.py
'testŭ.py': I/O Error: [Errno 2] No such file or directory: 'testŭ.py'


(In case the character after 'test' and before '.py' isn't showing up 
correctly, it's chr(65901), 'GREEK ACROPHONIC TROEZENIAN FIVE HUNDRED'.)