Construct a where clause when using the .SelectLayerByAttribute_management( in pyhhon

[DavidMcKelly]

Hi

Can somebody please help me to construct a where clause using a variable when using the arcpy.SelectLayerByAttribute_management( in pyhon.

1. Here is some of my code:

while row:
    print row.MESO_ID
    SelStr = '"' +'\"MESO_ID\" = ' + "'" +row.MESO_ID + "'" + '"'
    print SelStr
    outfeat = "p"+row.MESO_ID

    # Selected features, from "lyr" wher MESO_ID = row.MESO_ID  
    arcpy.SelectLayerByAttribute_management("lyr", "NEW_SELECTION", '"' +'\"MESO_ID\" = ' + "'" +row.MESO_ID + "'" + '"')
    
    # Write the selected features to a new featureclass
    arcpy.CopyFeatures_management("lyr", outfeat)

    row = rows.next()

2. When I run the script the SelStr prints the correct string but it keep on giving me an error at the:
     
    arcpy.SelectLayerByAttribute_management("lyr", "NEW_SELECTION", '"' +'\"MESO_ID\" = ' + "'" +row.MESO_ID + "'" + '"')
    
line.

3. I have also test it by entering the " "Meso_ID = '2010_20316' " value. This works perfect but since there are 25000 mesos, I cannot do them manually.  

Any ideas please?

Regards
David

[markdenil]

You seem to be trying to run the SelectLayerByAttribute_management tool while inside a cursor.
The cursor will lock the file, will it not, preventing the tool from getting access to the feature class?

I would suggest using the cursor to build a list of MESO_IDs in the feature class,
and then using the list to feed a loop that performs each selection by attibute.

By the by, using python's format substitution can make for much neater code
than concatenating with plus signs, and all those triple quotes...

[BruceBacia]

Mark's suggestion of using the cursor to build a list and iterating through the list will greatly improve the stability of the code.  Something like below should work (haven't tested it)

import arcpy
import os

folder = r'C:\Your Desired Output Path'
rows = arcpy.SearchCursor(lyr)
list = []
nullList = ['',' ','None']
for row in rows:
    mesoID = str(row.getValue('MESO_ID'))
    if mesoID not in nullList:    
        list.append(mesoID)
del row
del rows

for item in list:
    item = ''.join(["'",item,"'"])
    query = ''.join(['\"MESO_ID\" = ',item])
    arcpy.SelectLayerByAttribute_management("lyr","NEW_SELECTION",query)
    outFC = os.path.join(folder,''.join([item.strip("'"),'.shp']))
    arcpy.CopyFeatures_management("lyr", outFC)

[BruceBacia]

instead of copy features you'll probably want to use featureClass to featureClass.  it looks like copy features requires that the feature class be in existence. 

import arcpy
import os

folder = r'C:\Your Desired Output Path'
rows = arcpy.SearchCursor(lyr)
list = []
nullList = ['',' ','None']
for row in rows:
    mesoID = str(row.getValue('MESO_ID'))
    if mesoID not in nullList:    
        list.append(mesoID)
del row
del rows

for item in list:
    item = ''.join(["'",item,"'"])
    query = ''.join(['\"MESO_ID\" = ',item])
    arcpy.FeatureClassToFeatureClass_conversion (lyr,folder, ''.join([item.strip("'"), '.shp']), query,'','')

[DavidMcKelly]

Thank you Bruce and Mark for your useful response. I used you advice and it works fine now.

Regards