Сложить элементы из всех списков внутри списка (быстро)

def sum_list(list_of_lists):
    return_lst = []
    for i in list_of_lists:
        for i2 in i:
            return_lst = return_lst + i2
    return return_lst

def linearize(lst):
    if len(lst)==0:
        return []
    elif type(lst[0]) is list:
        return linearize(lst[0])+linearize(lst[1:])
    else:
        return [lst[0]]+linearize(lst[1:])
        
print(linearize([[[1,2], [3,4,5], [6]], [[7,8], [9], [10]]]))

def foo(iterable):
    try:
        result = []
        for x in iterable:
            result.extend(foo(x))
        return result
    except TypeError:
        return [iterable]
        
assert [1, 2, 3, 4, 5, 6, 7, 8, 9, 10] == foo([[[1,2], [3,4,5], [6]], [[7,8], [9], [10]]])

n = [[[1,2], [3,4,5], [6]], [[7,8], [9], [10]]]
fun = lambda x: str(x).translate(str.maketrans(',', ' ', '[]'))
s = list(map(int, fun(n).split()))
print(s)

from itertools import chain
 
 
def foo(a):
  return list(chain(*map(chain.from_iterable, a)))

import re
 
lst = [[[1, 2], [3, 4, 5], [6]], [[7, 8], [9], [10]]]
print(*map(int, re.findall(r'-?\d+', str(lst))))

import time
import re
 
lst = [[[1,2], [3,4,5], [6]], [[7,8], [9], [10]]]*500000
 
t1 = time.time()
res = map(int, re.findall(r'-?\d+', str(lst)))
t2 = time.time()
 
res = map(int, str(lst).translate(str.maketrans(',', ' ', '[]')).split())
t3 = time.time()
print(t2-t1, t3-t2)

print(res)

lst = [[[1, 2], [3, 4, 5], [6]], [[7, 8], [9], [10]]] # * 500000

print(*res)

import time
 
def sum_list_old(list_of_lists):
    return_lst = []
    for i in list_of_lists:
        for i2 in i:
            return_lst = return_lst+i2
    return return_lst
 
def sum_list(list_of_lists):
    return_lst = []
    for i in list_of_lists:
        for i2 in i:
            return_lst.append(i2)
    return return_lst
 
 
 
lst = [[[1,2], [3,4,5], [6]], [[7,8], [9], [10]]]*5000
 
lt = time.time()
s = sum_list_old(lst)
print("Old",(time.time()-lt)*1000, "мсек.")
 
 
lt = time.time()
s = sum_list(lst)
print("New",(time.time()-lt)*1000, "мсек.")