feat(python): Allow use of Python types in cs.by_dtype and col

[alexander-beedie]

Consistency/ergonomics; we accept Python types in most places already (eg: Schema, schema_overrides, etc), but were missing integration in the cs.by_dtype selector and col. This adds support for both.

Note

Selecting Python types that map to multiple Polars dtypes, such as int, float, datetime, or timedelta will select all the related Polars dtypes (eg: matching on int is equivalent to matching on all signed/unsigned Polars integer dtypes).

Example

from datetime import datetime
import polars.selectors as cs
import polars as pl

df = pl.DataFrame(
    {
        "idx": [],
        "dt1": [],
        "dt2": [],
    },
    schema_overrides={
        "idx": pl.UInt32,
        "dt1": pl.Datetime("ms"),
        "dt2": pl.Datetime(time_zone="Asia/Tokyo"),
    },
)

df.select(cs.by_dtype(datetime))
# shape: (0, 2)
# ┌──────────────┬──────────────────────────┐
# │ dt1          ┆ dt2                      │
# │ ---          ┆ ---                      │
# │ datetime[ms] ┆ datetime[μs, Asia/Tokyo] │
# ╞══════════════╪══════════════════════════╡
# └──────────────┴──────────────────────────┘

df.select(pl.col(int))
# shape: (0, 1)
# ┌─────┐
# │ idx │
# │ --- │
# │ u32 │
# ╞═════╡
# └─────┘

[codecov]

Codecov Report

Attention: Patch coverage is 86.11111% with 5 lines in your changes missing coverage. Please review.

Project coverage is 79.01%. Comparing base (f43a7d4) to head (e0df706).
Report is 4 commits behind head on main.

Files with missing lines	Patch %	Lines
py-polars/polars/functions/col.py	87.87%	2 Missing and 2 partials ⚠️
py-polars/polars/selectors.py	66.66%	0 Missing and 1 partial ⚠️

Additional details and impacted files

@@            Coverage Diff             @@
##             main   #20491      +/-   ##
==========================================
- Coverage   79.02%   79.01%   -0.01%     
==========================================
  Files        1563     1563              
  Lines      220596   220626      +30     
  Branches     2492     2502      +10     
==========================================
+ Hits       174317   174334      +17     
- Misses      45706    45718      +12     
- Partials      573      574       +1     

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