error in SelectLayerByAttribute

[ElaineKuo]

Hello

System: ArcGIS 9.3
pythonWin: 2.5

Problem 1:
Using SelectLayerByAttribute but error showed:
ExecuteError: ERROR 000358: Invalid expression

Please kindly help indicate the mistake in the query code.
Also, a shape file is attached for trial.
Thanks a lot.

 ##Script Name: Delete rows ##Description: delete selected rows ##Created By: Elaine Kuo ##Date: 04/05/2012  #Import standard library modules import arcgisscripting import os  #Create the Geoprocessor object gp = arcgisscripting.create(9.3)  #Set the input workspace #GP.workspace = sys.argv[1] #Set the workspace. gp.Workspace= "G:/temp"  #Set the output workspace #outWorkspace = sys.argv[2] #Set the workspace. List all of the feature classes in the dataset outWorkspace= "G:/temp/test"  #Get a list of the featureclasses in the input folder fcs = gp.ListFeatureClasses()  # Loop through every item in the list that was just generated for fc in fcs:      # Break out the name, no path or extension, using the describe object.     desc = gp.describe(fc)     featureName = desc.name      # Make featureclasses as layers     gp.OverWriteOutput = 1     gp.toolbox = "Data Management"     gp.MakeFeatureLayer("geor0313_p.shp","geor0313_p_lyr")          #Get a list of the fields in the featureclass     fields = gp.ListFields("geor0313_p_lyr", "C*", "String")      # Loop through every item in the list that was just generated      for field in fields:          gp.toolbox = "Data Management"               # Select records to be deleted (C*, i.e. C7658)         query = "\"C*\" = 'R'"         gp.SelectLayerByAttribute("geor0313_p_lyr", "ADD_TO_SELECTION", query)          # Delete selected records         gp.deleterows("geor0313_p_lyr")              #Validate the new feature class name for the output workspace.     outFeatureClass = outWorkspace + os.sep +GP.ValidateTableName("geor0313_p_lyr",outWorkspace)       

[BruceNielsen]

The where clause in selectlayerbyattribute does not recognize wildcard characters. You need to use the field variable that you're creating in the inner loop instead. Try this:

query = "\"%s\" = 'R'" % field

This will insert the field variable into the query expression each time the loop executes.

[ElaineKuo]

Hello,

system arcGIS 9.3

Thanks for the response.
However, the same error still occurred after modifying the code as below.
Please kindly help and thanks.

##Script Name: Delete rows
##Description: delete selected rows
##Created By: Elaine Kuo
##Date: 04/05/2012

#Import standard library modules
import arcgisscripting
import os

#Create the Geoprocessor object
gp = arcgisscripting.create(9.3)

#Set the input workspace
#GP.workspace = sys.argv[1]
#Set the workspace.
gp.Workspace= "G:/temp"

#Set the output workspace
#outWorkspace = sys.argv[2]
#Set the workspace. List all of the feature classes in the dataset
outWorkspace= "G:/temp/test"

#Get a list of the featureclasses in the input folder
fcs = gp.ListFeatureClasses()

# Loop through every item in the list that was just generated
for fc in fcs:

    # Break out the name, no path or extension, using the describe object.
    desc = gp.describe(fc)
    featureName = desc.name

    # Make featureclasses as layers
    gp.OverWriteOutput = 1
    gp.toolbox = "Data Management"
    gp.MakeFeatureLayer("geor0313_p.shp","geor0313_p_lyr")
    
    #Get a list of the fields in the featureclass
    fields = gp.ListFields("geor0313_p_lyr", "C*", "String")

    # Loop through every item in the list that was just generated 
    for field in fields:

        gp.toolbox = "Data Management"
     
        # Select records to be deleted (C*, i.e. C7658)
        query = "\"%s\" = 'R'" % field
        gp.SelectLayerByAttribute("geor0313_p_lyr", "ADD_TO_SELECTION", query)

        # Delete selected records
        gp.deleterows("geor0313_p_lyr")
        
    #Validate the new feature class name for the output workspace.
    outFeatureClass = outWorkspace + os.sep +GP.ValidateTableName("geor0313_p_lyr",outWorkspace)


    

[FabianBlau]

I guess field is a Field Object, not a String. Check this with gp.addMessage(type(field)).
So try:

query = "\"%s\" = 'R'" % field.Name

[ElaineKuo]

Thanks a lot.
You are right.
Please kindly explain why it works with "query = "\"%s\" = 'R'" % field.Name" instead of "query = "\"%s\" = 'R'" % field"
Also, please kindly help how to run gp.addMessage(type(field)) using PythonWin for a beginner. 🙂

[FabianBlau · Accepted solution]

In arcgisscripting 9.3 ListFeatureClasses() returns not a string but an object.
http://webhelp.esri.com/arcgisdesktop/9.3/index.cfm?TopicName=ListFields_method.

This object is like a container for severals varaibles and functions (for a  detailed explanation of objects read some smart books;) http://en.wikipedia.org/wiki/Object_%28computer_science%29)
One of the attributes is the fieldname -> http://webhelp.esri.com/arcgisdesktop/9.3/index.cfm?TopicName=Field_properties.


Use AddMessage when you start a script from a toolbox.
Use print starting a script in python.

print type(field)

[ElaineKuo]

Thanks a lot.

How to mark that you helped answer my questions 😮

[FabianBlau]

There is a button on the right side (sign in first) :D.