Turtle Island: A Utility Kit for Polars Expressions

This weekend, I started building a Python package called Turtle Island, which collects some of my ideas for helper functions aimed at reducing boilerplate when writing Polars expressions.

Currently, Turtle Island offers the following nine utilities:

• case_when() – A cleaner and more readable way to construct chained conditional logic in Polars.
• make_index() – Creates a virtual row index as a Polars expression, without materializing it as a column.
• bucketize_lit() – Assigns literal values to rows in a round-robin pattern based on their index.
• bucketize() – A more general version of bucketize_lit() that cycles through multiple Polars expressions, enabling advanced use cases with dynamic column values.
• is_every_nth_row() – Identifies every n-th row using a modulo operation on the row index.
• move_cols_to_start() – Reorders selected columns to appear at the beginning of the DataFrame.
• move_cols_to_end() – Reorders selected columns to appear at the end of the DataFrame.
• make_hyperlink() – Generates HTML anchor (<a>) tags from text and url columns for rendering clickable links.
• make_tooltip() – Creates HTML tooltips from label and tooltip columns for hoverable text display.

Here’s a quick example that uses ti.is_every_nth_row() to build a Polars expression suitable for styling tables interactively with Great Tables:

import polars as pl
from great_tables import GT, loc, style
from great_tables.data import countrypops

import turtle_island as ti

df_pd = countrypops.sample(10).loc[:, ["country_name", "year", "population"]]
df_pl = pl.from_pandas(df_pd)
row_expr = ti.is_every_nth_row(3)

(
    GT(df_pl)
    .tab_style(style=style.fill("lightblue"), locations=loc.body(rows=row_expr))
    .tab_style(style=style.fill("papayawhip"), locations=loc.body(rows=~row_expr))
    .opt_stylize(style=3, color="pink")
)

Disclaimer

This post was drafted by me, with AI assistance to refine the content.