Putting polars API extensions in dedicated module - How to import from target module?

Question

I want to extend polars API as described in the docs, like this:

@pl.api.register_expr_namespace("greetings")
class Greetings:
    def __init__(self, expr: pl.Expr):
        self._expr = expr

    def hello(self) -> pl.Expr:
        return (pl.lit("Hello ") + self._expr).alias("hi there")

    def goodbye(self) -> pl.Expr:
        return (pl.lit("Sayōnara ") + self._expr).alias("bye")

If I were to put the actual registration in a dedicated module (extensions.py), how am I supposed to import the methods from the respective class from within another module?

Going with the dataframe example in the docs, let's say I put the following code in a module called target.py.
I need to make the greetings-namespace available. How can I do it, i.e. how excactly should the import look like?

pl.DataFrame(data=["world", "world!", "world!!"]).select(
    [
        pl.all().greetings.hello(),
        pl.all().greetings.goodbye(),
    ]
)

Answer 1

You could just import extensions(assuming that the file is relative) in your target.py file to register the greetings namespace.

import polars as pl
import extensions # noqa: F401

pl.DataFrame(data=["world", "world!", "world!!"]).select(
    [
        pl.all().greetings.hello(),
        pl.all().greetings.goodbye(),
    ]
)

See also:

• polars-xdt