input: Write a function to check if a given number is an Armstrong number. If the number is an Armstrong number, return True. Otherwise, return False. An Armstrong number (also known as a narcissistic number) is a number that is the sum of its own digits each raised to the power of the number of digits.
  assert is_armstrong_number(153)==True
  assert is_armstrong_number(9474)==True
  assert is_armstrong_number(123)==False
  assert is_armstrong_number(8208)==True
  assert is_armstrong_number(9)==True
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