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closing excel application

Hung Jung Lu hungjunglu at yahoo.com
Sat Oct 18 13:09:22 EDT 2003 
"federico" <maschio_77 at hotmail.com> wrote in message news:<bmqrof$feo$1 at lacerta.tiscalinet.it>...
> When I close an excel application opened from a python program with .Close()
> methood , in tasks manager is still present 'excel.exe' process and if I
> open manually an excel applicaion I have a transparent excel window... my os
> is win 2000 pro... Which is the right way to close an excel applicatio from
> python?
> Thanks

The "right way" would be:

import win32com.client
import pythoncom
app = win32com.client.Dispatch('Excel.Application')
app.Visible = 1
...
print pythoncom._GetInterfaceCount()
app = None
print pythoncom._GetInterfaceCount()
pythoncom.CoUninitialize()

Pythoncom holds and manages the reference count. Which, you cannot
tweak with. (At least that's the intention of Mark Hammond... you
don't have access to the Release() method of the IUnknown interface.)
Therefore, ideally, you should catch all exceptions in your program,
and exit your Python program gracefully and invoke the
CoUninitialize() method to release all references to COM objects. That
is, your program is should not fail due to unhandled exceptions...
otherwise you will have dangling reference to COM objects, which you
cannot recover in new sessions of Python.

But the world is never ideal. :)

Here are a few "solutions". I hope others can contribute more.

(1) Simply kill the dangling Excel by hand from the task manager.
(2) Really, really, really make sure you use exception handling in
your program, and always exit your program gracefully by invoking
pythoncom.CoUnintialize().
(3) Find out the process id, and kill the dangling process before
anything else. The windows APIs provided by Mark Hammand may allow
this, but I have used instead the tlist.exe and kill.exe executables
from outside Python (you can launch them using os.system() or some
other ways of executing system command. I remember having problems
with Windows 98, though, some piping issues, but after adding one more
little file it was solved.)
(4) Write yourself a little COM program in C/C++ to invoke the
Release() method of the IUnknown() interface. You might even be able
to do this from using Thomas Heller's ctypes module without actually
programming in C/C++. I never tried it, though.

Of course the "right way" is alternative (2). I'd like to hear other
people's solutions.

--------------------

The Dispatch() late binding method is deceivingly easy to use, but
once you start to use it, you will realize that there are a lot of
issues. Using COM programming this way is best limited to simple,
routine tasks. Of course, that's just my opinion.

Hung Jung
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