input: Write a function to determine 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. Return True if the number is an Armstrong number, else return False. If the input number is empty then return False.
  assert is_armstrong_number(153)==True
  assert is_armstrong_number(9474)==True
  assert is_armstrong_number(123)==False
  assert is_armstrong_number(1253)==False
  assert is_armstrong_number(0)==False
output: def is_armstrong_number(num):
      if num is None or num == "":
          return False
      num_str = str(num)
      num_digits = len(num_str)
      sum_of_powers = sum(int(digit) ** num_digits for digit in num_str)
      return sum_of_powers == num