compare all the numbers in the list and return when there is a change in direction

def compare(a):
  b = []
  for i in range(len(a) - 1):
    if a[i] > a[i + 1]:
      b.append(-1)
    elif a[i] < a[i + 1]:
      b.append(1)
    else:
      b.append(0)
  return b
      
compare([1, 2, 3, 2, 1])