input: Write a python function to check if a number is an Armstrong number.
  assert is_armstrong(153) == True
  assert is_armstrong(9474) == True
  assert is_armstrong(123) == False
  assert is_armstrong(370) == True
output: def is_armstrong(number):
      digits = [int(digit) for digit in str(number)]
      power = len(digits)
      return sum(digit ** power for digit in digits) == number