input: from typing import List
  
  def is_armstrong_number(num: int) -> bool:
      """ Check if a given number is an Armstrong number.
      An Armstrong number is a number that is the sum of its own digits each raised to the power of the number of digits.
      For example, 153 is an Armstrong number because 1^3 + 5^3 + 3^3 = 153.
      >>> is_armstrong_number(153)
      True
      >>> is_armstrong_number(123)
      False
      """
output:     digits = [int(d) for d in str(num)]
      power = len(digits)
      return num == sum(d ** power for d in digits)