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How to get fields from GPValueTable feature classes in UpdateParamters function, arcpy.Describe throws error while we input model builder variable(which is out put from other tool)

Question asked by ssontineni_G2 on Jul 25, 2019

Below is the sample code which throws error when used in model builder and set input from other tool

class CombinedTool(object):
    def __init__(self):
        """Define the tool (tool name is the name of the class)."""
        self.label = "CombinedLRTool"
        self.description = "CombinedTool"
        self.canRunInBackground = False
        self.params = arcpy.GetParameterInfo()
    def getParameterInfo(self):
        """Define parameter definitions"""

        in_tables = arcpy.Parameter(
            displayName="Input Layers",
            name="InputLayers",
            datatype="GPFeatureLayer",
            parameterType="Required",
            direction="Input")

        in_seg = arcpy.Parameter(
            displayName="Seg Layers",
            name="in_seg",
            datatype="GPValueTable",
            # parameterType="Optional",
            direction="Input")
        in_seg.columns = [["GPTableView", "layer"]]

        testvalue = arcpy.Parameter(
            displayName="Test Field",
            name="testvalue",
            datatype="GPString",
            direction="Input")

        params = [in_tables,in_seg,testvalue]
        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."""       
        lyrdscr = arcpy.Describe(parameters[1].value[0][0])
        parameters[2].value = str([f.name for f in lyrdscr.fields])       

        return

    def updateMessages(self, parameters):
        """Modify the messages created by internal validation for each tool
        parameter.  This method is called after internal validation."""
        return

    def execute(self, parameters, messages):


        return

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