import pprint

def registerTreat(lis): #lis = a list of parameters
    lSize = len(lis)
    if lSize == 0 or lSize == 1 or lSize == 2:
        print('error')
    elif lSize == 3:
        try:
            t[lis[0]][lis[1]] = lis[-1]
        except:
            try:
                t[lis[0]] = {}
                t[lis[0]][lis[1]] = lis[-1]
            except:
                print('error 1')
    elif lSize == 4:
        try:
            t[lis[0]][lis[1]][lis[2]] = lis[-1]
        except:
            try:
                t[lis[0]][lis[1]] = {}
                t[lis[0]][lis[1]][lis[2]] = lis[-1]
            except:
                try:
                    t[lis[0]] = {}
                    t[lis[0]][lis[1]] = {}
                    t[lis[0]][lis[1]][lis[2]] = lis[-1]
                except:
                    print('error 2')
    #elif lsize == 5
        #etc
    #elif lsize == 6
        #etc
    #elif lsize == 7
        #etc
    else:
        print('function error')
    return

#example usage:
t = {}
value = 0.3
stage = 'pre'
registerTreat(['treatment','subtreatment', stage, value])
pprint.pprint(t)

# sometimes the output will be:
# {'treatment': {'subtreatment': {'pre': 0.3}}}

# and sometimes it will be:
# {'treatment': {'subtreatment': {'pre': [0.3]}}}

# I never call the function like this: registerTreat(['treatment','subtreatment', stage, [value]])