input: Write a function to check if a given number is an Armstrong number. An Armstrong number is a number that is equal to the sum of its own digits each raised to the power of the number of digits in the number. Return True if the number is an Armstrong number, otherwise return False. 
  assert is_armstrong_number(153)==True
  assert is_armstrong_number(370)==True
  assert is_armstrong_number(9474)==True
  assert is_armstrong_number(12345)==False
  assert is_armstrong_number(9475)==False
output: def is_armstrong_number(num):
      digits = str(num)
      power = len(digits)
      sum_of_powers = sum(int(digit) ** power for digit in digits)
      return sum_of_powers == num