Driving Excel from Python in Windows

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

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.
• Same book, free sample chapter Advanced Python and COM covers makepy in detail.
• Tutorials
• win32com documentation, I suggest you read this first.

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!

Check out the DataNitro project (previous name IronSpread). It is a Python plug-in for Excel.

I wrote python class that allows working with Excel via COM interface in Windows http://sourceforge.net/projects/excelcomforpython/

The class uses win32com to interact with Excel. You can use class directly or use it as example. A lot of options implemented like array formulas, conditional formatting, charts etc.