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I've been having a problem with arcpy in that the simple line:

arcpy.SelectLayerByAttribute_management ("TEMP_LINES")

produces this response: Runtime error : ERROR 000358: Invalid expression Failed to execute (SelectLayerByAttribute).

I've worked out that this error only occurs when a cursor is set, like this:

lineCursor = arcpy.UpdateCursor("TEMP_LINES","","","combined_i")

Can I not use select by attribute and the cursor or do I have one of them set up wrong?

EDIT: whole code:

arcpy.MakeFeatureLayer_management (Lines,"TEMP_LINES")

lineCursor = arcpy.UpdateCursor("TEMP_LINES","","","combined_i")

for row in lineCursor:
    arcpy.SelectLayerByAttribute_management ("TEMP_LINES")
    arcpy.SelectLayerByLocation_management (Polygons, "INTERSECT", "TEMP_LINES")
    arcpy.FeatureClassToFeatureClass_conversion (Polygons, "temp_polys")
    polyCursor = arcpy.SearchCursor("temp_polys")
    blocks_list = []
    for row in cursor:
        blocks_list.append(row.getValue("BLOCK"))
    blocks_str = ', '.join(blocks_list)
    lineCursor.BLOCK = blocks_str
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  • 1
    You don't provide a valid expression for the Select Layer by Attribute GP tool. You only provide the layer name which is not enough. – Alex Tereshenkov Dec 13 '13 at 11:09
  • 1
    without the cursor on this selects all. It doesnt work with any expression with the cursor on – whatahitson Dec 13 '13 at 11:17
  • Can you provide the whole chunk of code you execute please? I am a bit confused in which sequence you have those rows. – Alex Tereshenkov Dec 13 '13 at 11:33
  • @AlexTereshenkov I've edited to include – whatahitson Dec 13 '13 at 11:48
  • i've tested your code succefully, without any problems, it seems that the problem is not located in SelectLayerByAttribute_management – geogeek Dec 13 '13 at 16:48
2

As stated by others you have not provided a selection criteria for arcpy.SelectLayerByAttribute_management(). Additionally using arcpy.SelectLayerByAttribute_management() within an Update Cursor is only going to apply to a single row and does not really make sense to do.

If I understand what you are trying to accomplish, I think you need to rework your logic in this script. Perhaps run the arcpy.SelectLayerByLocation_management() previous to creating your cursors and use a where_clause as an argument to your arcpy.UpdateCursor to limit the number of records that you are searching and updating against.

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1

The SelectLayerByAttribute_management tool in your script is trying to select all features within the feature layer, whereas the cursor accesses one row at a time within the feature. If you would still like to use the tool within the cursor then there is a bit of an adjustment needed. I should make mention that this adjustment assumes the field "combined_i" is not unique.

lineCursor = arcpy.UpdateCursor("TEMP_LINES","","","combined_i; unique_field")
cols = arcpy.ListFields("TEMP_LINES")

for row in lineCursor:
    for col in cols:
        if col.name == "unique_field":
            objstr = row.getValue(col.name)
            arcpy.SelectLayerByAttribute_management("TEMP_LINES", "NEW_SELECTION", ("%s = %s" % (col.name, objstr)))
    .
    .
    .

Allow me to explain the additional code in more detail:

cols = arcpy.ListFields("TEMP_LINES")
    for col in cols:
        if col.name == "unique_field":
            objstr = row.getValue(col.name)

First, list all fields in "TEMP_LINES", then loop through the fields and find a field named "unique_field". If true then set objstr equal to the value of "unique_field" in the current row.

            arcpy.SelectLayerByAttribute_management ("TEMP_LINES", "NEW_SELECTION", ("%s = %s" % (col.name, objstr)))

Instead of trying to select all features in "TEMP_LINES" this will only select the feature with the unique value in "unique_field" at the current row.

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