Python: How to (not) keep a COM-object persistent in memory after closing the parent application?

Question

i am working on a (pretty big) Python/Tkinter-application (Python 2.7 under Windows 7) which (among many other things) calls Matlab via the COM-interface. The basic structure of the Matlab/COM-part is like this:

import Tkinter
import pythoncom
import win32com.client

class App( object ):

    def __init__( self, parent ):
        Tkinter.Button( root, text="Start Matlab", command=self.start_matlab ).grid()

    def start_matlab( self ):
        self.matlab = win32com.client.Dispatch( "Matlab.Application" )

root = Tkinter.Tk()
App( root )
root.mainloop()

The behaviour i observe with this simplified code is: Running the application and clicking the button creates a Matlab-Instance (opens a Matlab-Command window), and when closing the Tkinter application also that Matlab-window and the corresponding entry in the Task-Manager disappear. Repeating the procedure, Matlab is started afresh. However, when i do "the same" with my "real" application, the Matlab instance persists after closing my application and, moreover, when i restart the application and run the part which "starts" Matlab, it just retrieves and uses the instance which remained in memory after quitting the first sessiong of my app. Unfortunately, i am not able to isolate a reasonably small code example showing the latter behavior:(

Does anybody have an idea what the reason for this is/could be?

How can one control whether a COM-object is killed or persists in memory when the parent Python application which created it is closed?

Answer 1

Here's how to explicitly remove the COM object, using Tkinter's protocol handler:

import Tkinter
import pythoncom
import win32com.client

class App( object ):

    def __init__( self, parent ):
        self.parent = parent #reference to root
        Tkinter.Button( root, text="Start Matlab", command=self.start_matlab ).grid()
        self.parent.protocol('WM_DELETE_WINDOW', self.closeAll) #protocol method

    def start_matlab( self ):
        self.matlab = win32com.client.Dispatch( "Matlab.Application" )

    def closeAll(self):
        del self.matlab       #delete the COM object
        self.parent.destroy() #close the window

root = Tkinter.Tk()
App( root )
root.mainloop()

Reference: Removing COM object from memory

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