On Windows, subprocess.call() fails with an exception if either the executable or any of the arguments contain upper level characters. See below:

>>> cmd = [ u'test_\xc5_exec.bat', u'arg1', u'arg2' ]
>>> subprocess.call(cmd)

Traceback (most recent call last):
  File "<stdin>", line 1, in <module>
  File "C:\Python25\lib\subprocess.py", line 443, in call
    return Popen(*popenargs, **kwargs).wait()
  File "C:\Python25\lib\subprocess.py", line 593, in __init__
    errread, errwrite)
  File "C:\Python25\lib\subprocess.py", line 815, in _execute_child
    startupinfo)
UnicodeEncodeError: 'ascii' codec can't encode character u'\xc5' in position 5: ordinal not in range(128)

Python's default character coding is 'ascii' which can't convert unicode > 127 into chars.

Forcing the unicode string to encode as 'iso-8859-1' 

eg.
subprocess.call(cmd.encode('iso-8859-1')) 

resolves the problem and runs the correct command.

Sorry, I should have been more specific. I'm looking for a general solution, not just one for characters in iso-8859-1. For instance, I need to execute a subprocess where the executable or the arguments may contain Japanese characters.

So another example would be:
cmd = [ u'test_\u65e5\u672c\u8a9e_exec.bat', u'arg1', u'arg2' ]
subprocess.call(cmd)

I tried to fix this problem using CreateProcessW.
(environment variables are still ANSI)

I don't know Python C API well, maybe I'm doing
something wrong. (I confirmed test_subprocess.py
passes)

We're having the same problem.  My quick fix was to patch subprocess.py
so the command line and executable are converted to the filesystem
encoding (mbcs).