Question

Hi! Fellow OCW students! I have a question about defining a list as a variable. For instance, look at this: S= postRetirement(savings,postRetireGrowthRates,guess)
The postRetirement function produces a list. I would like to define this list as a variable so that I could use it flexibly. However, once I printed S, it had nothing - None. I tried S+=(postRetirement(savings,postRetireGrowthRates,guess, ) which didn't work neither. How do I fix this? Thanks!