Project Euler 34 # Digit Factorials in Python

Question

145 is a curious number, as 1! + 4! + 5! = 1 +たす 24 +たす 120 =わ 145.

Find the sum of all numbers which are equal to the sum of the factorial of their digits.

Note: as 1! = 1 and 2! = 2 are not sums they are not included.

from time import time
def fact(n):
 """returns factorial of n."""
 total = 1
 for number in range(2, n + 1):
 total *= number
 return total
def fact_curious(n, factorials={1:1, 2:2}):
 """Assumes n is the range to check for curious numbers.
 generates curious numbers within n range."""
 for number in range(3, n):
 try:
 if sum(factorials[int(digit)] for digit in str(number)) == number:
 yield number
 except KeyError:
 for digit in str(number):
 factorials[int(digit)] = fact(int(digit))
 if sum(factorials[int(digit)] for digit in str(number)) == number:
 yield number
if __name__ == '__main__':
 start_time1 = time()
 print(sum(fact_curious(100000)))
 print(f'Time: {time() - start_time1}')

• Peilonrayz: Please tag all Python questions with python, if you only have python-3.x then your question is more likely to go unanswered.

Answer 1

1. There is math.factorial function. So no need to reinvent it.
2. Using try/except for control flow is a bad practice. It's better to explicitly check whether a list contains a value using the condition if int(digit) in factorials. It also will eliminate the code duplication in except branch.
3. It's even better to pre-calculate all factorials for digits from 0 to 9. Anyway, you will reuse them all a lot of times.