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notepad.exe forms a side-by-side assembly with COMCTL32.DLL. So
SystemRoot must be included in the environment. The following example
works with Python 2.5.2 on Windows XP.
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import struct, subprocess
import os
command = 'C:\\WINDOWS\\NOTEPAD.EXE'
env = {'FOO': 'bar', 'SystemRoot': os.environ['SystemRoot']}
p = subprocess.Popen(command, env=env)
p.wait()
err = struct.unpack('I', struct.pack('i', p.returncode))[0]
print '%x (%d)'%(err, err)
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I would suggest Popen adds SystemRoot to env if it is not present.