Complete windows in pandas rolling

Question

I'm trying to create complete windows using the rolling function of pandas (a complete window is a window with the same size as the window argument of the rolling function).

Consider the following code snippet -

df = pd.DataFrame({'X': [1]*10,
                   'Y': 'a'})
df.loc[5:,'Y'] = 'b'

which yields the following dataframe-

    X   Y
0   1   a
1   1   a
2   1   a
3   1   a
4   1   a
5   1   b
6   1   b
7   1   b
8   1   b
9   1   b

Iterating the 3 elements size windows-

for win in df.groupby(["Y"]).rolling(3):
    print(win.shape[0])

1
2
3
3
3
1
2
3
3
3

Is it possible to get only 3 length size windows without using a win.shape[0] == 3 condition?

Thanks a lot.