As that file is being read in, the Python interpreter will be executing the lines 14 and 15 which defines and assigns the 'spi' variable, compiling and saving away for later use the class defined from line 17 and then executing line 31 which closes the 'spi' variable. You are not doing anything in between with the 'spi' variable that you create in line 14. Even if you later have executable code that does something with the 'Simulation' class, the 'spi'variable will be long gone.
Further, the class use of the 'spi' variable will be local to the class and not refer to the outer 'spi' variable.
Susan