This is what finally worked for me. /ASYNC was generating ERROR #00: (sin descripción de error)

set var0 ="python"
set var1 ="/path/to/python.py"
set var2 ="/path/to/file.xlsx"
set var3 ="/path/where/csv/file/goes/"

SET args = 3
SET args(1)=var1
SET args(2)=var2
SET args(3)=var3 w var0_" "_var1_" "_var2_" "_var3,!

W $ZF(-100 ,"/SHELL /LOGCMD" , var0 , .args)