How to add a duration to datetime in Python polars

Question

Update: This was fixed by pull/5837

shape: (3, 3)
┌─────────────────────┬─────────┬──────────────┐
│ dt                  ┆ seconds ┆ duration0    │
│ ---                 ┆ ---     ┆ ---          │
│ datetime[μs]        ┆ f64     ┆ duration[μs] │
╞═════════════════════╪═════════╪══════════════╡
│ 2022-12-14 00:00:00 ┆ 1.0     ┆ 1µs          │
│ 2022-12-14 00:00:00 ┆ 2.2     ┆ 2µs          │
│ 2022-12-14 00:00:00 ┆ 2.4     ┆ 2µs          │
└─────────────────────┴─────────┴──────────────┘

---

I want to add a duration in seconds to a date/time. My data looks like

import polars as pl

df = pl.DataFrame(
    {
        "dt": [
            "2022-12-14T00:00:00", "2022-12-14T00:00:00", "2022-12-14T00:00:00",
        ],
        "seconds": [
            1.0, 2.2, 2.4,
        ],
    }
)

df = df.with_columns(pl.col("dt").cast(pl.Datetime))

Now my naive attempt was to to convert the float column to duration type to be able to add it to the datetime column (as I would do in pandas).

df = df.with_columns(pl.col("seconds").cast(pl.Duration).alias("duration0"))

print(df.head())

┌─────────────────────┬─────────┬──────────────┐
│ dt                  ┆ seconds ┆ duration0    │
│ ---                 ┆ ---     ┆ ---          │
│ datetime[μs]        ┆ f64     ┆ duration[μs] │
╞═════════════════════╪═════════╪══════════════╡
│ 2022-12-14 00:00:00 ┆ 1.0     ┆ 0µs          │
│ 2022-12-14 00:00:00 ┆ 2.2     ┆ 0µs          │
│ 2022-12-14 00:00:00 ┆ 2.4     ┆ 0µs          │
└─────────────────────┴─────────┴──────────────┘

...gives the correct data type, however the values are all zero.

The documentation is kind of sparse on the topic, any better options?

Answer 1

Update: The values being zero is a repr formatting issue that has been fixed with this commit.

pl.duration() can be used in this way:

df.with_columns(
   pl.col("dt").str.to_datetime()
   + pl.duration(nanoseconds=pl.col("seconds") * 1e9)
)

shape: (3, 2)
┌─────────────────────────┬─────────┐
│ dt                      ┆ seconds │
│ ---                     ┆ ---     │
│ datetime[μs]            ┆ f64     │
╞═════════════════════════╪═════════╡
│ 2022-12-14 00:00:01     ┆ 1.0     │
│ 2022-12-14 00:00:02.200 ┆ 2.2     │
│ 2022-12-14 00:00:02.400 ┆ 2.4     │
└─────────────────────────┴─────────┘