Why does .split in python not work on double bracket list?

I’m trying to understand why a double bracket list throws an error when using .split().
If I can’t get rid of the double brackets, what are other ways to split both double and single bracket lists?

example :

y = (['3801 - 2', '123 + 49'])
print(type(y))
for i in y:
    print(i.split(' '))

output:

<class 'list'>
['3801', '-', '2']
['123', '+', '49']

While

x = ([['3801 - 2', '123 + 49']])
print(type(x))
for i in x:
    print(i.split(' '))

output:

<class 'list'>
AttributeError: 'list' object has no attribute 'split'

>Solution :

Because when you have a list inside a list.
The iteration unravel only the outermost list, whose only element is another that does not support the split method.
You either use a nested loop:

for j in y:
    for i in j:
        i.split()

or access the first element:

for i in y[0]:
    i.split()