ValueError: 0 is not in list

return n.index(find_max_number(n))

def find_maximum(n):
         b = find_max_number(n)
         return n.index(b)

    def find_max_number(n):
            middle = len(n)//2
            if len(n) == 1 :
                return (n[0])
            if len(n)>2:
               if n[middle] > n[middle-1] and n[middle] > n[middle+1] :
                return (n[middle])
            if (n[middle-1] < n[middle]):
              return find_maximum(n[middle:])
            else :
              return find_maximum(n[:middle])

def find_max_number(numbers):
    max_ = float('-inf')
    for number in numbers:
        if number > max_:
            max_ = number
    return max_

def find_maximum(numbers):
    max_ = float('-inf')
    max_index = None
    for index, number in enumerate(numbers):
        if number > max_:
            max_ = number
            max_index = index
    return max_index

n = [2, 3, 4, 5]

def greatest_num_index(n):
    return n.index(max(n))

print(greatest_num_index(n))

3

def max_num(n):
    greatest_num = n[0]
    for item in n:
        if item > greatest_num:
            greatest_num = item
    return greatest_num