iterating through a shapefile

Question

I'm new to geoprocessing with Python (but with a basic knowledge of Python) and have been trying to loop through a shapefile to perform analysis on each polygon in the shapefile.  I have seen references to looping through directories. etc. but haven't been able to translate them to working with polygons within a shapefile.

Thanks,
Mike

Using ArcGIS 9.3 on XP.

MikeKnowles · Answer

In addition to the while row: change, I needed to specify the fields I wanted to print.

while row:
    print row.POLYS_DD_, row.polys_dd_i
    row = rows.Next()

DarrenWiens2 · Answer

A cursor "returns an enumeration object that will, in turn, hand out row objects". I'm not quite sure why (I started with Python in ArcGIS 10), but in 9.3 I think it likes "while row:" rather than "for row in rows:".

MikeKnowles · Answer

I've written the following code based on "Writing Geoprocessing Scripts with ArcGIS" but am getting an error which I can't figure out. What is Python storing the data as (string, list, etc)? Has there been changes to how ArcGIS interprets the code?

Using Python 2.5.1; ArcGIS 9.3; Windows XP.

import arcgisscripting

GP = arcgisscripting.create(9.3)
GP.overwriteoutput = 1

GP.workspace = "C:\USER\FLATHER\great_plains_corridor\experimental"

rows = GP.SearchCursor("C:\USER\FLATHER\great_plains_corridor\experimental\polys_dd.shp")
row = rows.reset()

row = rows.Next()

for row in rows: # just in case, the following two lines are indented in the code but didn't appear indented in the preview
 print row(0)
 row = rows.Next()

The error is:
Traceback (most recent call last):
 File "C:\Python25\Lib\site-packages\pythonwin\pywin\framework\scriptutils.py", line 310, in RunScript
 exec codeObject in __main__.__dict__
 File "C:\USER\FLATHER\great_plains_corridor\experimental\script3.py", line 23, in <module>
 for row in rows:
TypeError: 'geoprocessing cursor object' object is not iterable