I have the following DF on which i am trying to construct a new column which is will be cum_sum.

I have the following DF on which i am trying to construct a new column which is will be cum_sum.

I have a Polars dataframe pydf in Python with a datetime column time1 that I’m passing to Rust.
In Rust I am calling code that works with epoch format, but afterwards it should return another dataframe with a datetime column time2_epoch in the same time unit and time zone as time1.