How to convert Date to timezone aware datetime in polars

Question

Let's say I have

df = pl.DataFrame({
    "date": pl.Series(["2022-01-01", "2022-01-02"]).cast(pl.Date)
})

How do I localize that to a specific timezone and make it a datetime?

I tried:

df.select(pl.col('date').cast(pl.Datetime(time_zone='America/New_York')))

but that gives me

shape: (2, 1)
┌────────────────────────────────┐
│ date                           │
│ ---                            │
│ datetime[μs, America/New_York] │
╞════════════════════════════════╡
│ 2021-12-31 19:00:00 EST        │
│ 2022-01-01 19:00:00 EST        │
└────────────────────────────────┘

so it looks like it's starting from the presumption that the naïve datetimes are UTC and then applying the conversion. I set os.environ['TZ']='America/New_York' but I got the same result.

I looked through the polars config options in the API guide to see if there's something else to set but couldn't find anything about default timezone.

Answer 1

As of polars 0.16.3, you can do:

df.select(
    pl.col('date').cast(pl.Datetime).dt.replace_time_zone("America/New_York")
)