nushell/crates/nu_plugin_polars/src
pyz4 7ca2a6f8ac
FIX polars as-datetime: ignores timezone information on conversion (#15490)
# Description
This PR seeks to fix an error in `polars as-datetime` where timezone
information is entirely ignored. This behavior raises a host of silent
errors when dealing with datetime conversions (see example below).

## Current Implementation
Timezones are entirely ignored and datetimes with different timezones
are converted to the same naive datetimes even when the user
specifically indicates that the timezone should be parsed. For example,
"2021-12-30 00:00:00 +0000" and "2021-12-30 00:00:00 -0400" will both be
parsed to "2021-12-30 00:00:00" even when the format string specifically
includes "%z".

```
$ ["2021-12-30 00:00:00 +0000" "2021-12-30 00:00:00 -0400"] | polars into-df | polars as-datetime "%Y-%m-%d %H:%M:%S %z"
╭───┬───────────────────────╮
│ # │       datetime        │
├───┼───────────────────────┤
│ 0 │ 12/30/2021 12:00:00AM │ 
│ 1 │ 12/30/2021 12:00:00AM │ <-- Same datetime even though the first is +0000 and second is -0400
╰───┴───────────────────────╯

$ ["2021-12-30 00:00:00 +0000" "2021-12-30 00:00:00 -0400"] | polars into-df | polars as-datetime "%Y-%m-%d %H:%M:%S %z" | polars schema
╭──────────┬──────────────╮
│ datetime │ datetime<ns> │
╰──────────┴──────────────╯
```

## New Implementation
Datetimes are converted to UTC and timezone information is retained.

```
$ "2021-12-30 00:00:00 +0000" "2021-12-30 00:00:00 -0400"] | polars into-df | polars as-datetime "%Y-%m-%d %H:%M:%S %z"
╭───┬───────────────────────╮
│ # │       datetime        │
├───┼───────────────────────┤
│ 0 │ 12/30/2021 12:00:00AM │
│ 1 │ 12/30/2021 04:00:00AM │ <-- Converted to UTC
╰───┴───────────────────────╯

$ ["2021-12-30 00:00:00 +0000" "2021-12-30 00:00:00 -0400"] | polars into-df | polars as-datetime "%Y-%m-%d %H:%M:%S %z" | polars schema
╭──────────┬───────────────────╮
│ datetime │ datetime<ns, UTC> │
╰──────────┴───────────────────╯
```

The user may intentionally ignore timezone information by setting the
`--naive` flag.
```
$ ["2021-12-30 00:00:00 +0000" "2021-12-30 00:00:00 -0400"] | polars into-df | polars as-datetime "%Y-%m-%d %H:%M:%S %z" --naive
╭───┬───────────────────────╮
│ # │       datetime        │
├───┼───────────────────────┤
│ 0 │ 12/30/2021 12:00:00AM │
│ 1 │ 12/30/2021 12:00:00AM │ <-- the -0400 offset is ignored when --naive is set
╰───┴───────────────────────╯

$ ["2021-12-30 00:00:00 +0000" "2021-12-30 00:00:00 -0400"] | polars into-df | polars as-datetime "%Y-%m-%d %H:%M:%S %z" --naive | polars schema
╭──────────┬──────────────╮
│ datetime │ datetime<ns> │
╰──────────┴──────────────╯
```

# User-Facing Changes
<!-- List of all changes that impact the user experience here. This
helps us keep track of breaking changes. -->
`polars as-datetime` will now account for timezone information and
return type `datetime<ns,UTC>` rather than `datetime<ns>` by default.
The user can replicate the previous behavior by setting `--naive`.

# Tests + Formatting
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Tests that incorporated `polars as-datetime` had to be tweaked to
include `--naive` flag to replicate previous behavior.

# After Submitting
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2025-04-04 09:43:21 -07:00
..
cache Polars: Minor code cleanup (#15144) 2025-02-19 09:47:21 -08:00
cloud Polars AWS S3 support (#14648) 2024-12-25 06:15:50 -06:00
dataframe FIX polars as-datetime: ignores timezone information on conversion (#15490) 2025-04-04 09:43:21 -07:00
lib.rs Adds polars list-contains command (#15304) 2025-03-12 08:25:03 -07:00
main.rs remove mimalloc allocator (#15317) 2025-03-15 09:32:55 -05:00