Compose

Function Composition

Combine multiple functions into a single function where each function's output becomes the next function's input. Functions execute right-to-left, following mathematical convention.

from better_py.functions import compose

double = lambda x: x * 2
increment = lambda x: x + 1

transform = compose(double, increment)
transform(5)  # 12: increment(5) → 6, then double(6) → 12

Reading right-to-left: increment runs first, then double. The result is a reusable transformation pipeline.

Left-to-Right Composition

Same as compose but executes left-to-right, which can be more intuitive for data pipelines.

from better_py.functions import compose_left

transform = compose_left(increment, double)
transform(5)  # 12

The execution order matches the reading order. Choose based on which direction feels natural for your use case.

Example: Validation Pipeline

Composition is useful for validation and data processing chains where each step is a pure, single-responsibility function:

def get_user(id):
    return {"id": id, "role": "admin"}

def check_perms(user):
    return user if user["role"] == "admin" else None

def check_auth(user):
    return user if user else None

validate = compose(check_auth, check_perms, get_user)
validate(123)  # Returns user object or None

Data flows through each function: get_user fetches the user, check_perms verifies admin role, and check_auth performs final validation.

Reference

Use compose when you need a reusable function. Use pipe to execute a chain immediately on a value.