arcpy.GetParameterAsText getting null value if used after arcpy.ExcelToTable_conversion

EvelynHsu

Hi everyone,

I recently discovered something strange with arcpy.GetParameterAsText() in a script tool. If the function is used after arcpy.ExcelToTable_conversion, somehow it will not receive any value from the toolbox.

I managed to reproduce this behaviour with the simplest script here.

import arcpy,os


if __name__ == '__main__':
    
    param1 = arcpy.GetParameterAsText(0) #gdb
    param2 = arcpy.GetParameterAsText(1)
    
    in_excel = r"E:\Python\ghzrzyw_202209\script\new.xlsx"
    fgdb = r"D:\Documents\ArcGIS\Default.gdb"
    out_table = os.path.join(fgdb, "testtable")
    arcpy.env.workspace = fgdb
    arcpy.env.OverwriteOutput = True
    sheet = "test"
    arcpy.ExcelToTable_conversion(in_excel, out_table, sheet)
    param3 = arcpy.GetParameterAsText(2)
    param4 = arcpy.GetParameterAsText(3)
    
    arcpy.AddMessage(param1)
    arcpy.AddMessage(param2)
    arcpy.AddMessage(param3)
    arcpy.AddMessage(param4)

 

The messages printed out only contain param 1 and 2.

Param 3 and 4 are NoneType values based on my further test, even though I provided some values as input. This happens regardless of the parameter data types configured with the script tool.

if I shift arcpy.ExcelToTable_conversion to after all the arcpy.GetParameterAsText(), then it all works fine. So it would seem that whether arcpy.GetParameterAsText is placed is the main culprit here.

My questions:

1. Is this an expected behaviour? I'm using ArcMap 10.8.1.
2. If so, does it mean that it's always recommended to use arcpy.GetParameterAsText() at the start of the script?

Thanks in advance!

DavidSolari

My general rule for writing script tools is to structure them like this:

 

 

def main(param0, param1, param2):
    return doSomethingWith(param0) + doOtherThingWith(param1 + param2)

if __name__ == "__main__":
    param0 = arcpy.GetParameterAsText(0)
    param1 = arcpy.GetParameterAsText(1)
    param2 = arcpy.GetParameterAsText(2)
    param3 = main(param0, param1, param2)
    arcpy.SetParameterAstext(3, param3)

 

 

This has two big benefits. First, you ensure all the parameters are yanked out of the aether and loaded into proper variables before you run your task. Second, you now have a main function that isn't strictly dependent on parameter state, which means you can write tests for it or call the function from other scripts without going through importing a toolbox.