I've seen from various questions on here that if an instance of Excel is opened from Python using:

xl = win32com.client.gencache.EnsureDispatch('Excel.Application')
xl.Visible = True
wb = xl.Workbooks.Open('Test.xlsx')

Then it does not load the default add-ins. I've tried forcing my add-in to load by instead running:

xl = win32com.client.gencache.EnsureDispatch('Excel.Application')
xl.Visible = True
addin = xl.Workbooks.Open('C:/path/addIn.xll')
wb = xl.Workbooks.Open('Test.xlsx')

However, when I do this an instance of Excel opens and I get a security message asking me to verify I want to open this add-in. If I click "Enable this add-in for this session only" Excel immediately closes and does not open my desired xlsx file.

Does anyone have any ideas how to force the add-in to load and then to allow me to open my file?

Thanks very much for your help!

I have actually managed to resolve this by borrowing something from this MSDN article relating to doing the same thing with VBA:

http://support.microsoft.com/default.aspx?scid=KB;en-us;q213489

The following now works perfectly:

xl = win32com.client.gencache.EnsureDispatch('Excel.Application')
xl.Visible = True
xl.RegisterXLL('C:/path/addin.xll')
wb = xl.Workbooks.Open('Test.xlsx')