Python Challenge - Sum of Prime Factors

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def sum_of_prime_factors(n): def is_prime(num): flag = True cap = int(num**0.5) for i in range(2,cap+1): if num % i == 0: flag = False break return flag divisor_list = filter(lambda x:n%x==0,range(2,n+1)) prime_divisor_list = filter(is_prime, divisor_list) return sum(prime_divisor_list) print(sum_of_prime_factors(91))

This is the first thing I cam up with.

The is_prime function is simple. Mathematically, you only need to test for divisors up to the square root of a number to check if it is prime.

divisor_list uses filtering to make a list (really a filter object) of the non-trivial divisors.

prime_divisor_list then filters divisor_list through the is_prime function.

I’m sure there are better ways, but this works without going overboard with looping.


Nice one, @joshjones0410200536.

Took the tack of deconstruction for this one…

def sum_of_prime_factors(n): def is_prime(x): if x < 2: return False for h in range(2, int(x ** 0.5) + 1): if x % h == 0: return False return True if is_prime(n): return n factors = [] for x in range(2, n // 2): if is_prime(x): while n % x == 0: factors.append(x) n /= x print (factors) return sum(factors) print(sum_of_prime_factors(91)) print(sum_of_prime_factors(191)) print(sum_of_prime_factors(88)) print(sum_of_prime_factors(216))

Would sure love to know the two tests it is not passing, any ideas?


Not sure if you’re still reading in this forum but I ran into they same problem with my code which only passed 3/5 tests at first. I compared the return values of my sum_of_prime_factors function to @joshjones0410200536 's and it seems the issue stems from ambiguous wording in the assignment. “return the sum of all of its prime factors” apparently means "add every prime factor to the sum exactly once, regardless of how many times it’s included in n" (e.g. sopf(8) = 2 != 6).

To fix this in your code, just change the while in line 11 to if and you should be good.


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And that is that. Great help! Thanks!

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