Aha, a list with a single element.  Good catch.  `pluck` and `get` don't handle this either:
```python
In [4]: get([0], range(3))
Out[4]: 0

In [5]: get([0], range(3), default=None)
Out[5]: (0,)

In [6]: list(pluck([0], [[1, 2], [3, 4]]))
Out[6]: [1, 3]

In [7]: list(pluck([0], [[1, 2], [3, 4]], default=None))
Out[7]: [(1,), (3,)]
```
Instead of `_simple_get(index)`, there could instead be `getter(ind, default=no_default)` (or `_getter` if you want the method to be private).  Although `getter(ind)` and `toolz.curry.get(ind)` are redundant, the former would be significantly faster.  `getter` could also be used by `pluck` and the other functions that may accept `key` function or indices.