Flattening a nested sequence

- list
- flatten

```
>>> a = [[1, 2, 3], [4, 5, 6]]
>>> b = [i for j in a for i in j]
# [1, 2, 3, 4, 5, 6]
```

Flattening a nested sequence

- list
- flatten

```
>>> a = [[1, 2, 3], [4, 5, 6]]
>>> b = [i for j in a for i in j]
# [1, 2, 3, 4, 5, 6]
```