[pywin32-bugs] [ pywin32-Bugs-3029949 ] Type information lost in enumeration of COM objects

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Bugs item #3029949, was opened at 2010-07-15 14:09
Message generated for change (Comment added) made by erikjanssen
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Category: com
Group: None
Status: Open
Resolution: None
Priority: 5
Private: No
Submitted By: Erik Janssen (erikjanssen)
Assigned to: Nobody/Anonymous (nobody)
Summary: Type information lost in enumeration of COM objects

Initial Comment:
I am using the pywin32-214.win32-py2.7.exe distribution.

I notice type information is not always available. In the following 3-line snippet 'SearchResult' is an enumerator of objects of a certain type'.

Coding it like this everything is fine and python knows the type of f:

        for i in range(0,result.SearchResults.Count):
            f = result.SearchResults.Item(i)
            print f.StartTime, "-", f.EndTime, f.Camera.CameraName

But in the following code, imho preffered, python complains about f being IUnknown and can't continue:

        for f in result.SearchResults:
            print f
            print f.StartTime, "-", f.EndTime, f.Camera.CameraName

In the generated files (gencache) all information seems to be available, as in the IDL of the COM component. 

I can supply lot's of additional information but I don't know what is making sense and what isn't.


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Comment By: Erik Janssen (erikjanssen)
Date: 2010-07-19 11:32

Message:
Here is the relevant IDL, assuming that is what you refer to:

223 interface IFootageDescriptionEnumerator : IDispatch
224 {
225 [id(DISPID_NEWENUM), propget] HRESULT _NewEnum([out, retval]
IUnknown** Enumerator);
226 [id(DISPID_VALUE), propget] HRESULT Item([in] VARIANT Index, [out,
retval] IFootageDescription **FootageInfo);
227 [id(0x00000001), propget] HRESULT Count([out, retval] long * Count);
228 }; 

I notice that another enumarator works fine in python, it is in the IDL
declared as:

131 interface ICameraEnumerator : IDispatch{
132 [id(0xfffffffc), propget] HRESULT _NewEnum([out, retval] IUnknown
**CameraEnum);
133 [id(00000000), propget] HRESULT Item([in] int Index, [out, retval]
ICamera **CameraInfo);
134 [id(00000000), propput] HRESULT Item([in] int Index, [in] ICamera
*CameraInfo);
135 [id(0x00000001), propget] HRESULT Count([out, retval] int *Count);

Hope that helps.

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Comment By: Mark Hammond (mhammond)
Date: 2010-07-15 18:40

Message:
Does the item have a _NewEnum method?  If so, how is it defined?  Otherwise
I am surprised IUnknown is returned - it should behave identically to when
you call Item() manually.

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