Splitting polygon with line using ArcPy?

Using ET Geowizard you can access the code for the Split Polygons with Polylines tool:

Here is the link to the script.

Alternatively, you can use ArcObjects to do this:

Cut Polygon Snippet

You may also use the one side buffer method described here.

If you want to go outside of ArcGIS then use geom.splitpolysbylines.

Personally i have never use it in a programme but i think you can access this commondline with python, please see the help for more details.

After the fact, I ended up creating my own ModelBuilder tool. I had forgot about this question and posted my solution to another similar question. For completeness, this is a repost of the answer:

I thought there must be a way to do this, so I created my what I believe to be a pretty good solution. I have posted it on the ArcGIS Resources site in the Community->Technical->Analysis & Geoprocessing->Analysis->Gallery.

The tool is called Split Polygons With Lines and requires an ArcInfo license because of some of the tools used within the model. Essentially what I did was create the minimum bounding box for the polygons and extend the lines to them. So using some ModelBuilder voodoo, I was able to turn the linework into polygons, which then I used Identity to split the original polys.

Please test it out and see if it works for you. In my (limited) tests it preserved attributes of the original polygons, and split only the existing polygons.