This works too:

```python
>>> from itertools import chain
>>> h = [['a', 'b', 'c', 'd'], [1, 2, 3, 4, 5], ['x', 'y'], ['foo']]
>>> list(chain(*map(chain, h)))
['a', 'b', 'c', 'd', 1, 2, 3, 4, 5, 'x', 'y', 'foo']
```

But unfortunately, its ~3x slower on a quick bench. boo.