Python Program to Find the Total Sum of a Nested List

[vlearner]

kindly guide me how should I proceed to solve this problem:
[[4,5],[7,8,[20]],100]

[ndc85430]

What have you tried? Hint: recursion is useful for problems like this.

[vlearner]

What have you tried? Hint: recursion is useful for problems like this.

def sum_nestedlist( l ):
   
    # specify that global variable is
    # referred to here in this function
    total = 0
     
    for j in range(len(l)):
       
        if type(l[j]) == list :
           
            # call the same function if
            # the element is a list
            sum_nestedlist(l[j])
        else:
           
            # if it's a single element
            # and not a list, add it to total
            total += l[j]  
             
    return total
             
print(sum_nestedlist([[1,2,3],[4,[5,6]],7]))

I checked this solution but I am not getting how the code works. can anyone explain the logic of code?

[menator01]

I don't know that i would use range on the list.
All though there are other ways but, maybe like this

mylist = [5,[5, 3, 3],5,5,5] # List of numbers

def sum_nested_list(mylist):
    # set the finction variable
    total = 0
    # Loop through the list checking for other list
    for num in mylist:
        if type(num) == list: # If a list is found, get the sum and add to total
            total += sum(num)
        else:
            total += num # else add the num to total
    return total # return the total

print(sum_nested_list(mylist))

Output:
31

[ndc85430]

You wrote code you don't understand?

[ibreeden]

Haha @menator01 , you are cheating! It would work fine if the list would remain limited to two dimensions, but it it is't. Vlearner had a list with a deeper nesting level: [[4,5],[7,8,[20]],100]. When you run your code on this list you get:

Error:
Traceback (most recent call last):
  File "/home/ibreeden/PycharmProjects/Forum/forum02.py", line 43, in <module>
    print(sum_nested_list(mylist))
  File "/home/ibreeden/PycharmProjects/Forum/forum02.py", line 33, in sum_nested_list
    total = total + sum(num)
TypeError: unsupported operand type(s) for +: 'int' and 'list'

@vlearner : your code is almost correct, you must change line 13 to

total += sum_nested_list(l[j])

... or else you lose the result of your recursive call.

I checked this solution but I am not getting how the code works. can anyone explain the logic of code?

The algorithm is straigtforward. If you would pass a list with integers to your function, it would return the sum of the numbers. But if one of the elements of the list is again a (nested) list, then this list is handled by the (recursive) call to the same function. In that case the returned sum must be added to the total.

[snippsat]

Python 🦄🥴❓

def flatten(seq):
    for item in seq:
        match item:
            case list():
                yield from flatten(item)
            case _:
                yield item

lst = [[1,2,3],[4,[5,6]],7]
print(sum(flatten(lst)))

Output:
28

[menator01]

Haha @menator01 , you are cheating! It would work fine if the list would remain limited to two dimensions, but it it is't. Vlearner had a list with a deeper nesting level: [[4,5],[7,8,[20]],100]. When you run your code on this list you get:

Error:
Traceback (most recent call last):
  File "/home/ibreeden/PycharmProjects/Forum/forum02.py", line 43, in <module>
    print(sum_nested_list(mylist))
  File "/home/ibreeden/PycharmProjects/Forum/forum02.py", line 33, in sum_nested_list
    total = total + sum(num)
TypeError: unsupported operand type(s) for +: 'int' and 'list'

@vlearner : your code is almost correct, you must change line 13 to

total += sum_nested_list(l[j])

... or else you lose the result of your recursive call.

I checked this solution but I am not getting how the code works. can anyone explain the logic of code?

The algorithm is straigtforward. If you would pass a list with integers to your function, it would return the sum of the numbers. But if one of the elements of the list is again a (nested) list, then this list is handled by the (recursive) call to the same function. In that case the returned sum must be added to the total.

You are correct.

[menator01]

Haha @menator01 , you are cheating! It would work fine if the list would remain limited to two dimensions, but it it is't. Vlearner had a list with a deeper nesting level: [[4,5],[7,8,[20]],100]. When you run your code on this list you get:

Error:
Traceback (most recent call last):
  File "/home/ibreeden/PycharmProjects/Forum/forum02.py", line 43, in <module>
    print(sum_nested_list(mylist))
  File "/home/ibreeden/PycharmProjects/Forum/forum02.py", line 33, in sum_nested_list
    total = total + sum(num)
TypeError: unsupported operand type(s) for +: 'int' and 'list'

@vlearner : your code is almost correct, you must change line 13 to

total += sum_nested_list(l[j])

... or else you lose the result of your recursive call.

The algorithm is straigtforward. If you would pass a list with integers to your function, it would return the sum of the numbers. But if one of the elements of the list is again a (nested) list, then this list is handled by the (recursive) call to the same function. In that case the returned sum must be added to the total.

You are correct.

This seems to work

mylist = [5,[5, [9,3], 3],10,8,5,[10, [5, [5,2]], 8]] # List of numbers

def sum_nested_list(mylist):
    # set the finction variable
    total = 0
    # Loop through the list checking for other list
    for num in mylist:
        if type(num) == list: # If a list is found, get the sum and add to total
            total += sum_nested_list(num)
        else:
            total += num # else add the num to total
    return total # return the total

print(f'Final total is {sum_nested_list(mylist)}')

Output:
Final total is 78