data_sum total(datareturn sum_so_far total sum_so_far int numbers main script function total data data_sum list int int int we now turn to the left hand side of the line in the main script this establishes name data_sum to attach to the value returned from the function call the name is defined in the main body fo the script and so is created in the script' namespace the name is attached to the value (integerthat was created by the function