Sum all Armstrong numbers within a range

armstrong.py

from decimal import Decimal
 
def is_armstrong_number(number):
    digits = Decimal(number).as_tuple.digits()
    exp = len(digits)
    return sum(d**exp for d in digits) == number
 
def sum_all_armstrong_numbers(start, end):
    start_, end_ = sorted([start, end])
    return sum(number for number in range(start_, end_+1)
               if is_armstrong_number(number))