user1816377 - 10 months ago 77

Python Question

I'm looking for method in python to sum a list of list that contain only integers.

I saw that the method

`sum()`

There is anything fit for me?

thank you

Answer

You can use `sum()`

with a generator expression here:

```
In [18]: lis = [[1, 2], [3, 4], [5, 6]]
In [19]: sum(sum(x) for x in lis)
Out[19]: 21
```

**or:**

```
In [21]: sum(sum(lis, []))
Out[21]: 21
```

`timeit`

comparisons:

```
In [49]: %timeit sum(sum(x) for x in lis)
100000 loops, best of 3: 2.56 us per loop
In [50]: %timeit sum(map(sum, lis))
100000 loops, best of 3: 2.39 us per loop
In [51]: %timeit sum(sum(lis, []))
1000000 loops, best of 3: 2.21 us per loop
In [52]: %timeit sum(chain.from_iterable(lis)) # winner
100000 loops, best of 3: 1.43 us per loop
In [53]: %timeit sum(chain(*lis))
100000 loops, best of 3: 1.55 us per loop
```

Source (Stackoverflow)