Magic ETL Python script

Hello. I can't find any example to run a Magic ETL Python script.

I have added a column. I want to populate it with a pythons script and it never works

in the schema tab I have added a new text column named : "Alias" and here is my script : 

# Import the domomagic package into the script 
from domomagic import *
# read data from inputs into a data frame
input1 = read_dataframe('dataset')
# write your script here

# i dont know how to add a property "Alias" to input1 : here is what i have tried :
input1["Alias"] = "test"

# write a data frame so it's available to the next action
write_dataframe(input1)

I know I can achieve it with a simple "Add constants" but I would like to know how to use python script.