CODEWITHSUNDEEP
pythonpython-3.x
Jack
Jack

Reputation: 3057

Finding the sum of a nested list of ints

import math
lists =  [1,[2,3],4]
total = 0
for i in range(len(lists)):
    total += sum(i)
print(total)

I want it to print,

>>>10

But throws an error.

I would like it to get it to add all numbers, including the ones within the nested if.

Upvotes: 4

Views: 4284

Answers (3)

Subham
Subham

Reputation: 411

numpy.hstack() function is used to stack the sequence of input arrays horizontally (i.e. column wise) to make a single array which is what we require in OP example

import numpy as np 

list1 =  [1,[2,3],4]
M = np.hstack(list1) 
print(np.sum(M))

gives

10

[Program finished]

Upvotes: 0

Faruk Sahin
Faruk Sahin

Reputation: 8726

You can use flatten function in the compiler.ast module to flatten the list. Then simply sum up all the elements.

>>> lists =  [1,[2,3],4]
>>> from compiler.ast import flatten
>>> sum(flatten(lists))
10

EDIT: Only works with Python 2.x

Upvotes: 6

karthikr
karthikr

Reputation: 99660

In your program, for i in range(len(lists)) - evaluates to 3 as the lists object has 3 element. and in the loop total += sum(i) it would try to do a int + list operation, which results in an error. Hence you need to check for the type and then add the individual elements.

def list_sum(L):
    total = 0  
    for i in L:
        if isinstance(i, list): 
            total += list_sum(i)
        else:
            total += i
    return total

This is @pavelanossov 's comment - does the same thing, in a more elegant way

sum(sum(i) if isinstance(i, list) else i for i in L)

Upvotes: 7

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