topic Re: Editing shapefiles with Python in Python Questions

Editing shapefiles with Python

CharlesGant — Sun, 01 Apr 2012 10:17:26 GMT

Hello folks. I had a post over on the general forum about how to round values using the field calculator. I got the answer I was looking for but was referred to this board to ask a question about python.

I have to edit a series of shapefiles (about 100). They all have the same field labels. I need to add a field, and then round a certain field we will call "X", to the nearest five, and populate the new field with those values. The formula I was given was "Round(/5.0, 0) * 5.0". I have a some experience working with arcpy and python, however I have never used it to modify a shapefile. Can someone help me out with the script I would use to do what I have described above so i can then write it into a loop and do the work on all my shapefiles. I can handle the loop part. Thanks!

Re: Editing shapefiles with Python

NareshPai — Sun, 01 Apr 2012 18:53:19 GMT

It would be useful to give the forum some code to start with. You may need arcpy.AddField_management and arcpy.CalculateField_management to get started with the loop.

Naresh Pai

Re: Editing shapefiles with Python

CharlesGant — Sat, 11 Dec 2021 12:40:48 GMT

Sorry about that. Here is what I have so far. For simplicity on the forum, I have just one shapefile in the code for now. If I can get help with the code to do what I want on one, I can build the for loop to do the rest with the remaining shapefiles in a list.

 
# Import modules
import arcpy
import math

# Local variables:
point_shp = "R:\\Tornado Research\\test\\SfcOA.shp"


newfield = R_WsdpSfc
input = "getclass(double(!WSPD_SFC!))" #Not sure how to get the input file in this line of code
expression = "round([input]/5.0, 0) * 5.0" #Not sure if this is the correct way of doing this line

# Process: Add Field
arcpy.AddField_management(point_shp, newfield, "DOUBLE", "", "", "25", "", "NON_NULLABLE", "NON_REQUIRED", "") # Works fine

# Execute CalculateField 
arcpy.CalculateField_management(point_shp, newfield, expression, "PYTHON") #Obviously this line is broken

The "Add Field" command works just fine, I just cant figure out the "Calculate Field" segment. Thanks Again!

Re: Editing shapefiles with Python

JakeSkinner — Mon, 02 Apr 2012 11:01:13 GMT

Try changing your expression variable to:

expression = "round(!WSPD_SFC!/5.0, 0) * 5.0"

Since the expression is quoted as a string, it will not read 'input' as a variable. It will read this as a string literal.

Re: Editing shapefiles with Python

CharlesGant — Mon, 02 Apr 2012 11:20:22 GMT

Try changing your expression variable to:
expression = "round(!WSPD_SFC!/5.0, 0) * 5.0"
Since the expression is quoted as a string, it will not read 'input' as a variable. It will read this as a string literal.

Wow, I dont know why I did not realize that! I completely overlooked it. That fixed it! I guess sometimes when you stare at this stuff for so long, eventually you just need a new set of eyes to look it over. Thanks Jake!