How to generate automatically the name of output parameters in a python script tool? [closed]

You should use arcpy.Describe() and/or the os.path Python module. For example:

import arcpy, os
input = arcpy.GetParameterAsText(0)
output_workspace = arcpy.Describe(input).path # the file path, or geodatabase for geodatabase datasets
suffix = 1
output_name = arcpy.Describe(input).baseName + "_" + suffix # the file base name + a suffix
arcpy.CopyFeatures_management(input, os.path.join(output_workspace, output_name))

You can also check for the existence of the output if you want to make sure it doesn't already exist, increment the suffix if it does, etc.

EDIT: Based on the example above, if you want to have this output_name value returned in the tool's interface as asked in your comment, you should modify the validation code:

def updateParameters(self):
  if self.params[0].value:
      output_workspace = arcpy.Describe(self.params[0]).path 
      suffix = 1
      output_name = arcpy.Describe(self.params[0]).baseName + "_" + suffix
      self.params[1].value = os.path.join(output_workspace, output_name)

  return

And your script should look like this:

 input = arcpy.GetParameterAsText(0)
 output = arcpy.GetParameterAsText(1)
 arcpy.CopyFeatures_management(input, output)

Don't forget to import all necessary modules in both codes.

Refer to Customizing script tool behavior, this is where the code comes from and there are other examples for other use cases.