Python

A few random notes on Python

About this page

I am using Python mostly for ESRI Geoprocessing. As I become more comfortable with it I am starting to branch out and use it for other things.

This page is not intended as a tutorial or repository of all Python knowledge. It contains random notes on how I am using Python and will change as I learn what works and does not work for me.

IDE

Komodo

I use ActiveState Komodo 4.x, which is not free but I think it's worth it. I think it's about $300. That is for a 'personal' license which means I have permission to install it on all my computers. I admire this approach - I only use one computer at a time. For free, they have a stunted editor "Open Komodo" but I need the debugger.

If you try the eval version you won't want to go back to PythonWin.

Eclipse

I looked at Eclipse for Python but it looked too rudimentary for a beginner. SWT is the widget set used in Eclipse, I am not sure if there are Python bindings for it. It might be a reason to delve into it further. If you are a Java programmer already using Eclipse that might also be a reason to try it with Python.

For the time being though I have made my pact with Komodo.

GUI

So far I have used Python for scripting operations such as geoprocessing. Now I am at the stage where I want to start designing GUI based applications especially ones that can be portable between Windows and Linux.

I want a nice tool to help me design the UI. Therefore I am looking at the following.

wxWindows http://wxwindows.org/ a portable GUI platform for forms based on GTK

wxWidgets http://wxwidgets.org/ the widgets used by wxWindows.

Some relevant Ubuntu packages

boa-constructor RAD tool http://boa-constructor.sourceforge.net/ (Application runs under Linux and Windows)

python-card GUI construction framework http://pythoncard.sourceforge.net/

python-wxglade GUI designer

python-wxtools

python-wxversion

Databases

From the ArcGIS perspective, I can access geodatabases using ArcObjects but for the frequent occasions when it runs out of gas, I can tap into the underlying databases.

For shapefiles I can use dbfpy to read and write the attributes, which are stored in the .dbf file.

For personal geodatabases I can tap into the MDB using either ODBC or OLEDB. See Accessing Personal Geodatabases with Python

For file geodatabases... well, ESRI has not released specs yet so I use PGDB's.

Geoprocessing

ESRI

Old notes:

This guy seems to have slogged through a lot of development with it and collected useful notes: http://www.ollivier.co.nz/support/python.shtm

I can add a new one to his list. I was getting error messages on setting gp.workspace = 'foo' where foo is a valid path. It's because the gp object was hanging around in pythonwin's memory. You should be able to say 'del gp' but I gave up and restarted pythonwin to fix it.

When working with ArcToolbox 9.1 and Python 2.1 I have been having lots of crashes in PythonWin. Using it on a computer with ActiveState 2.4.3 I have not been experiencing the same problems. I am going to try installing 2.4x without removing 2.1 so I can fall back on it... I followed the instructions above.

It still crashes. Oh joy. It does not even crash faster.

Open source

How about geoprocessing with OGR/GDAL? Will that do it for me?

Getting Python 2.4 and GDAL without disrupting the ESRI installation... See also Howard Butler's site.

FWtools installs a GUI called OpenEV_FW and a shell environment. It comes with python 2.3.4 which is old. I think Frank does this because it's stable and test with his tools. Going to a newer version means the DLL won't work so you'd need to compile your own.

23-Aug-2006 Python+OGR probably not worth messing with right now. From the OGR site: The Python API isn't really well documented at this time, but parallels the C/C++ APIs. The interface classes can be browsed in the pymod/ogr.py (simple features) and pymod/osr.py (coordinate systems) python modules. The pymod/samples/assemblepoly.py sample script is one demonstration of using the python API.