Driving Excel from Python in Windows

Question

Hi Folks,

We have various spreadsheets that employ deliciously complicated macros and third party extensions to produce complicated models. I'm working on a project that involves slightly tweaking various inputs and seeing the results. Rather than doing this by hand or writing VBA, I'd like to see if I can write a python script to drive this. In other words, the python script will start up, load the excel sheet, and then interact with the sheet by making minor changes in some cells and seeing how they affect other cells.

So, my question is twofold:

• What is the best library to use to drive excel from python in such fashion?

• Where's the best documentation/examples on using said library?

Cheers, /YGA

Answer 1

I've done this by using pywin32. It's not a particularly pleasant experience, since there's not really any abstraction; it's like using VBA, but with python syntax. You can't rely on docstrings, so you'll want to have the MSDN Excel reference handy (http://msdn.microsoft.com/en-us/library/aa220733.aspx is what I used, if I remember correctly. You should be able to find the Excel 2007 docs if you dig around a bit.).

See here for a simple example.

from win32com.client import Dispatch

xlApp = Dispatch("Excel.Application")
xlApp.Visible = 1
xlApp.Workbooks.Add()
xlApp.ActiveSheet.Cells(1,1).Value = 'Python Rules!'
xlApp.ActiveWorkbook.ActiveSheet.Cells(1,2).Value = 'Python Rules 2!'
xlApp.ActiveWorkbook.Close(SaveChanges=0) # see note 1
xlApp.Quit()
xlApp.Visible = 0 # see note 2
del xlApp

Good luck!

Answer 2

For controlling Excel, use pywin32, like @igowen suggests.

Note that it is possible to use static dispatch. Use makepy.py from the pywin32 project to create a python module with the python wrappers. Using the generated wrappers simplifies development, since for instance ipython gives you tab completion and help during development.

Static dispatch example:

x:> makepy.py "Microsoft Excel 11.0 Object Library"
...
Generating...
Importing module
x:> ipython

> from win32com.client import Dispatch
> excel = Dispatch("Excel.Application")
> wb = excel.Workbooks.Append()
> range = wb.Sheets[0].Range("A1")
> range.[Press Tab]
range.Activate                 range.Merge
range.AddComment               range.NavigateArrow
range.AdvancedFilter           range.NoteText
...
range.GetOffset                range.__repr__
range.GetResize                range.__setattr__
range.GetValue                 range.__str__
range.Get_Default              range.__unicode__
range.GoalSeek                 range._get_good_object_
range.Group                    range._get_good_single_object_
range.Insert                   range._oleobj_
range.InsertIndent             range._prop_map_get_
range.Item                     range._prop_map_put_
range.Justify                  range.coclass_clsid
range.ListNames                range.__class__
> range.Value = 32
...

Documentation links:

• The O'Reilly book Python Programming on Win32 has an Integrating with Excel chapter.
• Tutorials
• win32com documentation, I suggest you read this first.

Answer 3

I worked on a home project last year that involves a client written as a Python Excel plug-in. The project is essentially an online database simplified for end-user access. The Excel plug-in allows users to query data out of the database to display in Excel.

I never got very far with the Excel plug-in and my code for it is a bit ugly. But, what I do have is under a BSD license and available via Bazaar at

http://www.launchpad.net/analyz/trunk

The client won't work since I don't have a public server running right now, but at least you can look at what I did with the code to get some ideas how this could work. The code will also show you how to build an MFC dialog in 100% Python.

If you have any trouble accessing the software or have any questions, contact me at [email protected].