How to find the arithmetic mean of array elements through recursion?

Question

Python

Wrote this, but there must be a more elegant way

test_list = [1, 4, 7]

def func(list1, a=0, b=0):
  if list1 == []:
    return 0

  b += list1[a]
  a += 1

  if a == len(list1):
    return b / a
  return func(list1, a, b)

print(func(test_list))

Answer 1

Think about how you can recursively calculate the sum. Further, the arithmetic mean is elementarily expressed in terms of the sum, and the sum is expressed in terms of the arithmetic mean. Here is the formula:
Avg(a1,a2,...an) = (Avg(a2,...an)*(n-1)+a1)/n