Getting zmin zmax of a raster parameter in a tool validation in ArcGIS Desktop 10.7 toolbox Python script

Question

I am developing a Python tool (my first one). The tool has 3 input parameters:

1. a raster
2. z min
3. z max

I am trying to get automatically z min and z max after the user specify the raster using the validation script but I got this error:

TypeError: expected a raster or layer

This is my code (commented lines are other attempts I tried without results):

def updateParameters(self):
"""Modify the values and properties of parameters before internal
validation is performed.  This method is called whenever a parameter
has been changed."""

if self.params[0].altered:
  if self.params[0].value:
    #rst_ds = self.params[0]
    rst_ds = self.params[0].value
    self.params[1].value = arcpy.Raster(rst_ds).minimum

    #self.params[2].value = arcpy.Raster(rst_ds.replace('\\','/')).maximum
    #arcpy.MakeRasterLayer_management(rst_ds, "rst_lyr")
    #self.params[1].value = arcpy.Raster("rst_lyr").minimum

return

Answer 1

You were almost there! Firstly ensure your parameters are their correct data type as shown below:

The correct code in the validation function updateParameters would be:

  def updateParameters(self):
    """Modify the values and properties of parameters before internal
    validation is performed.  This method is called whenever a parameter
    has been changed."""
    if self.params[0].altered:
      if self.params[0].value:
        rst_ds = self.params[0].valueAsText
        ra = arcpy.Raster(rst_ds)
        self.params[1].value = ra.minimum
        self.params[2].value = ra.maximum
    return