Add-In Combo Box: populate with specific field's values and pass selection to select by attribute

Question

I checked Passing Selection from Combo Box into Definition Query using Python AddIn?, but I am still stuck on code/syntax.

I created a simple add-in with a button that clips and exports tax parcels within a selected feature from the a grid. However, I want to include a combo box to prompt the user to enter or select the grid number rather than use the mouse to select from the data frame. It should accept user input in a drop-down bar listing the features for the GRID field in the grid layer and pass it as a definition query into 'select by attributes'. I'm still new to Python and am stuck on the selection process.

Script listed below:

import arcpy
import pythonaddins

log = file('//geodata/gisdata/Workspace/GIS/Rachel/Python_AddIn/Taddin4/Install/AddIn.log', 'a')
mxd = arcpy.mapping.MapDocument('current')
clipLayer = arcpy.mapping.Layer('Tax Map Small Grid')
gridCursor = arcpy.SearchCursor(clipLayer)
gridNums = []
for row in gridCursor:
    gridNums.append(row.GRID)

class Taddin4Box(object):
    """Implementation for Taddin4_addin.combobox (ComboBox)"""
    def __init__(self):
        self.items = sorted(gridNums)
        self.editable = True
        self.enabled = True
        self.dropdownWidth = 'WWWWWW'
        self.width = 'WWWWWW'
    def onSelChange(self, selection):
        clipLayer.definitionQuery = '"GRID"' + "=" + "'" + selection + "'"
        print >>log, 'About to select...'
        N = arcpy.SelectLayerByAttribute_management(clipLayer, "NEW_SELECTION", clipLayer.definitionQuery)
        print >>log, 'Selection completed...'
        return N
        arcpy.RefreshActiveView()
        pass
    def onEditChange(self, text):
        pass
    def onFocus(self, focused):
        pass
    def onEnter(self):
        pass
    def refresh(self):
        pass

class Taddin4button(object):
    """Implementation for Taddin4_addin.button (Button)"""
    def __init__(self):
        self.enabled = True
        self.checked = False
    def onClick(self):
        outpath = '//geodata/gisdata/Workspace/GIS/Rachel/Python_AddIn/Taddin4/Install/CAD/Shapefiles/'
        CADpath = '//geodata/gisdata/Workspace/GIS/Rachel/Python_AddIn/Taddin4/Install/CAD/'
        parcelsLayer = arcpy.mapping.Layer('Tax Parcels City')
        for row in gridCursor:
            gridField = row.getValue("GRID")
            num = gridField.replace('-','')
            print >>log, 'GRID number is: ' + gridField
        clipFC = 'TaxGrid'+num
        arcpy.Clip_analysis(parcelsLayer, clipLayer, outpath + clipFC)
        arcpy.ExportCAD_conversion(clipFC, "DWG_R2013", CADpath+gridField+'.dwg', "IGNORE_FILENAMES_IN_TABLES", "", "")
        print >>log, 'Done.'
        arcpy.SelectLayerByAttribute_management(clipLayer, "CLEAR_SELECTION")
        log.close()
        pass

Answer 1

The definition query worked once I changed it to this:

"GRID = '" + selection + "'"

instead of this: '"GRID"' + "=" + "'" + selection + "'"

Also, I removed the print statements from the ComboBox onSelChange function and opened the log file within the Button onClick function (instead of at the top of the script). I also re-defined the mxd, clipLayer, and gridCursor variables again within the Button onClick function (copied and pasted those lines).