Add list values together in python?

Question

I have a list that looks like this:

['9,7,4', '10,5,6,5,5', '10,8,5,3,0', '8,4,2']

How can i convert the numbers to ints and add the individual string values together?

So the desired out put would be

['20','31','26','14']

Answer 1

Use map to convert the splitted (using , as the delimiter) string values into int followed by a list comprehension to get the sum

input_list = ['9,7,4', '10,5,6,5,5', '10,8,5,3,0', '8,4,2']
output = [str(sum(map(int, x.split(',')))) for x in input_list]
print (output)

Output

['20', '31', '26', '14']

I edited after seeing your desired output as strings

Answer 2

[sum(map(int, group.split(','))) for group in l]

Answer 3

Someone mentioned eval , so I think you should take this a step further with a safe-eval alternative:

>>> import ast
>>> [ast.literal_eval(v.replace(',', '+')) for v in lst]
>>> [20, 31, 26, 14]

One thing I like about this answer is that it is purely a non-functional approach (no map inside a list comprehension, which is fine but I don't really believe in mixing paradigms).

Obviously this will only work if you have numbers separated by a single comma, without any leading or trailing characters and invalid arithmetic expressions.

I leave the conversion to string as an exercise.

Answer 4

If all strings are in this format you can try to use eval function - this will convert numbers into tuples from which you can count sum.

>>> l = ['9,7,4', '10,5,6,5,5', '10,8,5,3,0', '8,4,2']
>>> sums = [sum(numbers) for numbers in map(eval, l)]
>>> sums
[20, 31, 26, 14]

If you want output list to contain strings these values can be easily mapped:

[str(value) for value in sums]
# or
map(str, sums)