[Python-Dev] UUID module (original) (raw)

Thomas Heller theller at python.net
Sat Jun 10 17:11:15 CEST 2006

Ka-Ping Yee wrote:

Finally, Phillip brought up PEAK:

PEAK's uuid module does this such that if win32all is present, you get a Windows GUID, or if you have a FreeBSD 5+ or NetBSD 2+ kernel you use the local platform uuidgen API. See e.g.: ...so i looked at PEAK's getnodeid48() routine and borrowed the Win32 calls from there, with a comment giving attribution to PEAK. Oh, and there is now a test suite that should cover all the code paths. This is all posted at http://zesty.ca/python/uuid.py now, documentation page at http://zesty.ca/python/uuid.html, tests at http://zesty.ca/python/testuuid.py .

(From http://zesty.ca/python/uuid.py:)

def win32_getnode(): """Get the hardware address on Windows using Win32 extensions.""" try: import pywintypes return int(pywintypes.CreateGuid()[-13:-1], 16) except: pass try: import pythoncom return int(pythoncom.CreateGuid()[-13:-1], 16) except: pass

This does not work, for several reasons.

  1. (pythoncom|pywintypes).CreateGuid() return a PyIID instance, which you cannot slice:

import pywintypes pywintypes.CreateGuid() IID('{4589E547-4CB5-4BCC-A7C3-6E88FAFB4301}') type(pywintypes.CreateGuid()) <type 'PyIID'> pywintypes.CreateGuid()[-13:-1] Traceback (most recent call last): File "", line 1, in ? TypeError: unsubscriptable object

So, you would have to change your code to 'str(pythoncom.CreateGuid())[-13:-1]'.

(BTW: Why does it first try pywintypes, the pythoncom?)

  1. These functions call to win32 CoCreateGuid function, which create a new uuid. As documented on MSDN, this calls the UuidCreate function which:

"The UuidCreate function generates a UUID that cannot be traced to the ethernet/token ring address of the computer on which it was generated."

In other words, the last 12 characters do not identify the mac address, in fact your function, if repaired, returns a different result each time it is called. See this link for further info:

http://msdn.microsoft.com/library/default.asp?url=/library/en-us/rpc/rpc/uuidcreate.asp

A possible solution, if you really need the mac address, is to call the UuidCreateSequential function where available (W2k, XP, ...), and UuidCreate on older systems (W98, ME). Link to MSDN: http://msdn.microsoft.com/library/default.asp?url=/library/en-us/rpc/rpc/uuidcreatesequential.asp

  1. Now that ctypes is part of Python, why not use it? This snippet of code displays the mac address of one of the ethernet adapters I have in my machine:

from ctypes import * import binascii

class UUID(Structure): fields = [("Data1", c_ulong), ("Data1", c_ushort), ("Data1", c_ushort), ("Data1", c_ubyte * 8)]

def CreateGuid(): uuid = UUID() if 0 == windll.rpcrt4.UuidCreateSequential(byref(uuid)): return str(buffer(uuid))

print binascii.hexlify(CreateGuid()[-6:])

It should be extended to also work on w98 or me, probably.

Thomas

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