Derive (default) value in ValueTable based on values in ValueTable of Python Toolbox using ArcPy?

Question

I am writing a Python Toolbox which needs Shapefiles (or Featureclasses) as input and calculates an output for each of the input files. I would like to have the possibility to rename the files in order to avoid an overwriting or an exception. My approach is to use a toolbox parameter of type GPValueTable with 2 columns. The input files is given in the first column (by the user) and I want the 2. column to be automatically filled by the base name without extension of the input file.

GUI Python Toolbox - on the left the file given by the user and on the right the automatically derived default autput name

Unfortunatelly, I am not able to fill the second column based on the first. I tried various ways already but here is a snipped of sample code:

 def getParameterInfo(self):
 """Define parameter definitions"""
 input_paths = arcpy.Parameter(
 displayName="Input files",
 name="in_paths",
 datatype="GPValueTable",
 parameterType="Required",
 direction="Input",
 multiValue=True)
 input_paths.columns = [['GPFeatureLayer','Eingabedatensatz'], ['GPString','Ausgabename']]
 output_path = arcpy.Parameter(
 displayName="Output path",
 name="out_path",
 datatype="DEFolder",
 parameterType="Required",
 direction="Input")
 params = [input_paths,output_path]
 return params
def isLicensed(self):
 """Set whether tool is licensed to execute."""
 return True
def updateParameters(self, parameters):
 """Modify the values and properties of parameters before internal
 validation is performed. This method is called whenever a parameter
 has been changed."""
 if parameters[0].value:
 new_vt = []
 gp_value_table = parameters[0].value
 vt_length = len(gp_value_table)
 if gp_value_table[vt_length-1][0] and not not gp_value_table[vt_length-1][1]:
 new_vt = [[v[0],v[2]] for v in gp_value_table]
 input_path = gp_value_table[vt_length-1][0]
 new_vt.append([vt_length-1,arcpy.Describe(input_path).baseName])
 parameters[0].value = new_vt
 return

In this case nothing happens and the 2. column remains emtpy. How can I - row by row - derive the default output name based on the input?

• Hornbydd: What version of ArcMap are you using, there are differences in the behaviour for this parameter type?
• user2132627: I'm currently using ArcMap 10.4.1

Answer 1

The only code you need to change is the code in your updateParameters()

def updateParameters(self, parameters):
 """Modify the values and properties of parameters before internal
 validation is performed. This method is called whenever a parameter
 has been changed."""
 # Create a ValueTable object and load it with current values from parameter 
 # which itself is a ValueTable
 vtab = arcpy.ValueTable(len(parameters[0].columns))
 vtab.loadFromString(parameters[0].valueAsText)
 # Create a list of the values in the parameter, this will be a list of lists
 aList = parameters[0].values
 # Step through list, extract basename and update row in ValueTable object
 for i,v in enumerate(aList):
 fc = v[0]
 bn = arcpy.Describe(fc).baseName
 newvalue = "'" + str(fc) + "'" + " " + "'" + bn + "'"
 vtab.setRow(i, newvalue)
 # Write the contents of ValueTable object back into the Parameter which will overwrite everything
 parameters[0].value = vtab.exportToString()
 return

• user2132627: That works as long as the user doesn't update the values manually. When changing the values the script automatically discards the changes.
• Hornbydd: You asked for column 2 to be automatically filled by the base name without extension of the input file. This is what the code does. You need to augment the script to include a check to see if a base name exists and if it is NOT the same (so they have manually edited it) then don't update that row. You should be able to work that out.