[python-win32] Python crash after win32com.client.CastTo?

[Mark Hammond]

> By inserting print statements into win32com/client/__init__.py, I've
> established that the crash is occuring in the call to
> self._oldobj_.InvokeTypes(...) in DispatchBaseClass._ApplyTypes_.

Unfortunately, _InvokeTypes_ is the main "entry point" for *all* COM calls
with type information.  As part of this call, Python packs all Python args
into VARIANTs, then makes the actual call to the COM object.

Thus, I see 2 possibilities:
* pythoncom has a bug in InvokeTypes, probably in arg packing or unpacking.
* The COM object has a bug once control has been passed to that.

If pythoncom does have such a bug, it is subtle - all other COM objects
generally work fine.  Also, the symptoms don't really match what Python
would do - the only thing I can see that would cause Python to "abort" like
that is a call to Py_FatalError - that does indeed call the C 'abort'
function, but will always cause some short error text to be printed before
termination.

I'm afraid that my guess is that it is the remote object.  If it happens
only after a CastTo, I suspect that something is going wrong there.  Even
though we "CastTo" an interface (IFMANWiffFile2 in this example), we are
*still* using IDispatch on the object.  If the remote object expected a
"real" interface rather than an IDispatch based one, or the CastTo source
object is incorrect, I could see how this could happen.

> If this is a bug in pywin, is this enough information to fix
> it? If not, how can I generate more helpful information?

I'm afraid it is tricky without a debug build of pywin32.

Mark