Adding 2 linked lists

The problem I have is to find the sum of 2 linked lists. Each linked list node contains 1 digit that represents a number.

My algorithm works but I was wondering if there is a more efficient (speed and memory wise) to solve this problem OR maybe some minor tweaks I can do to reduce space and runtime.

Example: 7 -> 5 -> 6 = 756

I am trying to find the sum of 2 linked lists.

def addlist(LL1, LL2):
    storage = []
    multiplier = 1
    total = 0
    while LL1 != None:
        storage.append(LL1.data)
        LL1 = LL1.next
    for i in storage[::-1]:
        total += i*multiplier
        multiplier *= 10
    storage = []
    multiplier = 1
    while LL2 != None:
        storage.append(LL2.data)
        LL2 = LL2.next
    for j in storage[::-1]:
        total += j*multiplier
        multiplier *= 10
    return total

Don't repeat yourself

Your method has the same code duplicated twice in it. You should always try to eliminate this kind of duplication, for example like this:

def addlists(LL1, LL2):
    return sumlist(LL1) + sumlist(LL2)

def sumlist(LL1):
    storage = []
    multiplier = 1
    total = 0
    while LL1 != None:
        storage.append(LL1.data)
        LL1 = LL1.next
    for i in storage[::-1]:
        total += i*multiplier
        multiplier *= 10
    return total

Simplify

The logic can be simplified, a lot:

def sumlist(ll):
    total = 0
    while ll:
        total *= 10
        total += ll.data
        ll = ll.next
    return total

I also simplified the None comparison, instead of if ll != None you can write simply if ll

Naming

The convention is to use lowercase variable names, so it would be better to change LL1 and LL2.

StackExchange Code Review Q#51258, answer score: 4