I want to have a function in my model that converts an arbitrary value to a percentage within that column's range. It would need to be dynamic. Right now I have:

def prob( Failure_Score ):

my_list = arcpy.da.TableToNumPyArray ("Failure_Score")

my_max = max(my_list)

percentage = (Failure_Score / my_max)*100

return percentage

but it returns nothing. Really any advice would be greatly appreciated.

Attached is a screencap with the two fields in question and the Calculate Field window.

Thanks!

Ignoring numpy for the moment, you can load your list via a SearchCursor: