input: Write a python function to check if a number is an Armstrong number.
  assert is_armstrong(153) == True
  assert is_armstrong(370) == True
  assert is_armstrong(371) == True
  assert is_armstrong(9474) == False
output: def is_armstrong(number):
      digits = [int(d) for d in str(number)]
      power = len(digits)
      armstrong_sum = sum(d ** power for d in digits)
      return armstrong_sum == number