Using win32com with multithreading

The answer from @Mauriusz Jamro ( https://stackoverflow.com/a/27966218/7733418 ) was really helpful. Just to add to it, also ensure that you do:

pythoncom.CoUninitialize ()

in the end so that there's no memory leak. You can call it somewhere after using CoInitialize() and before your process ends.

If you want to use win32com in multiple threads you need to do a little bit of work more as COMObject cannot be passed to a thread directly. You need to use CoMarshalInterThreadInterfaceInStream() and CoGetInterfaceAndReleaseStream() to pass instance between threads:

import pythoncom, win32com.client, threading, time

def start():
    # Initialize
    pythoncom.CoInitialize()
     
    # Get instance
    xl = win32com.client.Dispatch('Excel.Application')

    # Create id
    xl_id = pythoncom.CoMarshalInterThreadInterfaceInStream(pythoncom.IID_IDispatch, xl)
 
    # Pass the id to the new thread
    thread = threading.Thread(target=run_in_thread, kwargs={'xl_id': xl_id})
    thread.start()

    # Wait for child to finish
    thread.join()

def run_in_thread(xl_id):
    # Initialize
    pythoncom.CoInitialize()
     
    # Get instance from the id
    xl = win32com.client.Dispatch(
            pythoncom.CoGetInterfaceAndReleaseStream(xl_id, pythoncom.IID_IDispatch)
    )
    time.sleep(5)


if __name__ == '__main__':
    start()

For more info see: https://mail.python.org/pipermail/python-win32/2008-June/007788.html