How to sum every n rows in python or pandas

There are similar questions to this but I could not find exactly same or an answer works for my question.

From my data, I divided A column by B column and I had results of 4000 rows not stored in data. I would like to take sum of every 100 rows such as from 0 to 100 (first 1000 rows) then 100 to 200 and store the new result as a new column in new data frame?

e.g

0        42
1        85
2        23
3        36
4        65
5        10
6        21
.
.
4000 

Thank you