GUID and ctypes

Hello,

I try to use the WinApi library powrprof.dll, but I cannot figure out
how to deal with the GUID.

I found a definition in comtypes and in the following example it works fine:
>>> array = ctypes.c_byte*8
>>> guid = GUID()
>>> guid.Data1 = 2709787400
>>> guid.Data2 = 13633
>>> guid.Data3 = 20395
>>> guid.Data4 = array(188,129,247,21,86,242,11,74)
>>> ctypes.windll.powrprof.PowerSetActiveScheme(None, ctypes.byref(guid))

But if I try the opposite example, I get the error ERROR_INVALID_PARAMETER:
>>> guid = GUID()
>>> ctypes.windll.powrprof.PowerGetActiveScheme(None, ctypes.byref(guid))
0
>>> str(guid)
'{003A66B8-0000-0000-0000-000000000000}'
>>> ctypes.windll.powrprof.PowerSetActiveScheme(None, ctypes.byref(guid))
87

Please tell me what's wrong - whether in the way I work with GUID,
ctypes or WinAPI.

Thank you very much,
-- 
Radek Holý
Czech republic

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