Sum the digits of a number
If you want to keep summing the digits until you get a single-digit number (one of my favorite characteristics of numbers divisible by 9) you can do:
def digital_root(n):
x = sum(int(digit) for digit in str(n))
if x < 10:
return x
else:
return digital_root(x)
Which actually turns out to be pretty fast itself...
%timeit digital_root(12312658419614961365)
10000 loops, best of 3: 22.6 µs per loop
Found this on one of the problem solving challenge websites. Not mine, but it works.
num = 0 # replace 0 with whatever number you want to sum up
print(sum([int(k) for k in str(num)]))
Both lines you posted are fine, but you can do it purely in integers, and it will be the most efficient:
def sum_digits(n):
s = 0
while n:
s += n % 10
n //= 10
return s
or with divmod
:
def sum_digits2(n):
s = 0
while n:
n, remainder = divmod(n, 10)
s += remainder
return s
Slightly faster is using a single assignment statement:
def sum_digits3(n):
r = 0
while n:
r, n = r + n % 10, n // 10
return r
> %timeit sum_digits(n)
1000000 loops, best of 3: 574 ns per loop
> %timeit sum_digits2(n)
1000000 loops, best of 3: 716 ns per loop
> %timeit sum_digits3(n)
1000000 loops, best of 3: 479 ns per loop
> %timeit sum(map(int, str(n)))
1000000 loops, best of 3: 1.42 us per loop
> %timeit sum([int(digit) for digit in str(n)])
100000 loops, best of 3: 1.52 us per loop
> %timeit sum(int(digit) for digit in str(n))
100000 loops, best of 3: 2.04 us per loop
This might help
def digit_sum(n):
num_str = str(n)
sum = 0
for i in range(0, len(num_str)):
sum += int(num_str[i])
return sum