Composition

Three small helpers for putting functions together. Nothing magic, they just read better than nested calls.

pipe

pipe threads a value through functions left to right. It replaces h(g(f(x))), which you have to read inside out.

from pyrula import pipe

pipe(
    "  Hello World  ",
    str.strip,
    str.lower,
    lambda s: s.replace(" ", "-"),
)   # "hello-world"

flow

flow is pipe without the value: it builds a reusable function out of the steps.

from pyrula import flow

slugify = flow(str.strip, str.lower, lambda s: s.replace(" ", "-"))

slugify("  Hello World  ")   # "hello-world"

partial

partial fixes some arguments up front and gives back a function waiting for the rest. Handy for dropping a configured function into a pipe or flow.

from pyrula import partial

def clamp(lo, hi, x):
    return max(lo, min(hi, x))

clamp_byte = partial(clamp, 0, 255)
clamp_byte(300)   # 255

Scala equivalent

flow is Scala’s f andThen g (or Function.chain); pipe is the pipe from scala.util.chaining (x.pipe(f)); partial is partial application, the same idea as currying a function and fixing its leading arguments.