Pandas rolling window with step equal to window size

I want to obtain the sum of the first four elements, then the sum of the next four ...

If you want a non-overlapping window, that's not a rolling window.

Instead, you can floor divide the index by your window size and group:

>>> s.groupby(s.index//4).sum()
0     6
1    22
2    38
3    54
dtype: int64

In case of a non-range index: s.groupby(np.arange(len(s)) // 4).sum()

P.S. I'm pretty sure there's a more idiomatic way to do this, but this is just what I thought of first. I'll update if I remember.