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Date: Tue, 07 Apr 2015 16:18:09 +0100
From: Tim Golden <mail@timgolden.me.uk>
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To: python-list@python.org
Subject: Re: Python library - WMI.py RegistryValueChangeEvent
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On 07/04/2015 15:52, Tim Golden wrote:
> On 07/04/2015 15:35, Khyati wrote:
>> On Tuesday, April 7, 2015 at 10:31:47 AM UTC-4, Chris Angelico wrote:
>>> On Wed, Apr 8, 2015 at 12:15 AM, Khyati wrote:
>>>> Thanks for taking a look, Chris.
>>>> The error trace:
>>>> traceback (most recent call last):
>>>>  File "MonitorRegistry.py", line 18, in <module>
>>>>    process_created = watcher()
>>>>  File "C:\Python27\lib\site-packages\wmi.py", line 1195, in __call__
>>>>    handle_com_error ()
>>>>  File "C:\Python27\lib\site-packages\wmi.py", line 241, in handle_com_error
>>>>    raise klass (com_error=err)
>>>> _wmi: <x_wmi: Unexpected COM Error (-2147352567, 'Exception occurred.', (0, u'SWbemPropertySet', u'Not found ', None, 0, -2147217406), None)>
>>>
>>> It looks to me like this is a thin wrapper around the underlying API
>>> call, and you're getting back an error from the lower-level services.
>>> The way this reads, there might well not be an
>>> HKLM\Software\Temp\Name; maybe the ValueName is what's wrong here?
>>>
>>> Someone somewhere knows more than I do, but if you can't find that
>>> someone here on python-list, you might be able to find some help on
>>> Stack Overflow or another mailing list, from people who know how to do
>>> this kind of thing in a different language. You'd have to translate
>>> their suggestions back into Python, but when the wrappers are thin
>>> enough, that's usually not too hard.
>>>
>>> ChrisA
>>
>> HKLM\Software\Temp\Name exists since the event is caught correctly only when I change that key.
>> i'll keep looking :)
>>
> 
> Hi, Khyati.
> 
> Unfortunately, extrinsic events don't come with much information. As you
> can see from the MSDN description:
> 
> https://msdn.microsoft.com/en-us/library/aa390355%28v=vs.85%29.aspx
> 
> they're not linked to WMI objects internally (which the intrinsic events
> are) so all they can do is echo back to you details of what changed --
> which will usually be the thing you were asking about in the first place!
> 
> So the Python wrapper doesn't receive any TargetInstance because it's
> not a *WMI* event as such, linked to a WMI object; rather, it's an
> external event which has provided a hook for WMI to hang on to.
> 
> In this specific case, you could use the WMI Registry provider to pick
> up the current value of that registry value, but that wouldn't tell you
> what was there before or anything else. In another case, the event might
> be about some entirely external system -- such as the
> SecurityViolationEvent in the MSDN example -- which provides no WMI
> interface beyond the event itself.
> 
> Feel free to ask more, either on this list or on the win32-specific
> Python list:
> 
> https://mail.python.org/mailman/listinfo/python-win32
> 
> (I'm not often free to answer questions so best to use the public forums
> where more people will be able to help).


Forgot to say: you can simplify your code a little as well:

<code>
import wmi

c = wmi.WMI(namespace="root/default")
watcher = c.RegistryValueChangeEvent(Hive="HKEY_LOCAL_MACHINE",
KeyPath=r"Software\\Temp", ValueName="Name")

event = watcher()

</code>

TJG