How to find the sum of a string in a list

Question

I have a list like this

['MGM', '1'], ['MGD', '1'], ['V1', '[0,2,0,1]'], ['AuD', '[0,0,0,1]']

in python. I want to find the sum of the lists that are strings like this:

['MGM', '1'], ['MGD', '1'], ['V1', '3'], ['AuD', '1']

Should I convert them to lists within the lists first? If so how would I go about this?

Trying my best to learn how to code for science.

Answer 1

Given:

s = [['MGM', '1'], ['MGD', '1'], ['V1', '[0,2,0,1]'], ['AuD', '[0,0,0,1]']]

The following will convert the second items to Python objects:

import ast
for sublist in s:
    sublist[1] = ast.literal_eval(sublist[1])

Result:

[['MGM', 1], ['MGD', 1], ['V1', [0, 2, 0, 1]], ['AuD', [0, 0, 0, 1]]]

Then convert them back with special handling for lists:

for sublist in s:
    if isinstance(sublist[1],list):
        sublist[1] = sum(sublist[1])
    sublist[1] = str(sublist[1])

Result:

[['MGM', '1'], ['MGD', '1'], ['V1', '3'], ['AuD', '1']]

Answer 2

This should do what you want. Explanation is in the comments.

import ast

# Create the list
myList = [['MGM', '1'], ['MGD', '1'], ['V1', '[0,2,0,1]'], ['AuD', '[0,0,0,1]']]

# Loop through each sublist
for num in myList:
    # try to convert the string to a list and sum it
    try:
        # This works by evaluating the string into a list object
        # Then summing the numbers in the list
        # then turning that number back into a string so it's like the rest
        num[1] = str(sum(ast.literal_eval(num[1])))
    # If it fails, it must just be a number, so ignore
    except TypeError:
        pass

print myList

Answer 3

>>> s = [['MGM', '1'], ['MGD', '1'], ['V1', '[0,2,0,1]'], ['AuD', '[0,0,0,1]']]

Since your data is a disaster, we'll use a helper function for the sum

>>> def mysum(L):
...     try:
...         return sum(L)
...     except TypeError:
...         return L
... 

can use JSON or literal_eval to decode the strings

>>> import json
>>> [[i, str(mysum(json.loads(j)))] for i, j in s]
[['MGM', '1'], ['MGD', '1'], ['V1', '3'], ['AuD', '1']]