katharos — Functional programming abstractions for Python.

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About this project

Katharos is a Python library that enhances functional programming with powerful abstractions. It features Monads, Applicatives, and Functors, alongside immutable data structures, enabling developers to write composable and type-safe code. Streamline your programming experience with elegant solutions for handling optional values and modeling errors.

Katharos is a powerful library designed for functional programming in Python, offering essential abstractions such as Monads, Applicatives, Functors, and immutable data structures. This enables developers to write composable and type-safe code with ease.

Core Features

Handle Optional Values: Safely deal with optional values without the need for tedious None checks:

from katharos.types import Maybe

result = Maybe[int].Just(5) | (lambda x: Maybe[int].Just(x * 2))  # Just(10)
nothing = Maybe[int].Nothing() | (lambda x: Maybe[int].Just(x * 2))  # Nothing()

Error Modeling: Effectively model errors as values instead of exceptions, allowing for clearer error handling:

from katharos.types import Result

def parse_int(s: str) -> Result[ValueError, int]:
    try:
        return Result.Success(int(s))
    except ValueError as e:
        return Result.Failure(e)

parse_int("42") | (lambda n: Result[ValueError, int].Success(n * 2))  # Success(84)
parse_int("??") | (lambda n: Result[ValueError, int].Success(n * 2))  # Failure(...)

Chaining Operations: Use do-notation to chain operations elegantly:

from katharos.types import Maybe
from katharos.syntax_sugar import do, DoBlock

@do(Maybe)
def lookup_discount(user_id: int) -> DoBlock[float]:
    user    = yield find_user(user_id)      # short-circuits on Nothing
    account = yield find_account(user)
    return account.discount

lookup_discount(42)  # Just(0.15) or Nothing()

Value Combination: Combine values seamlessly with the Semigroup operator:

from katharos.types import ImmutableList

ImmutableList([1, 2]) @ ImmutableList([3, 4])  # ImmutableList([1, 2, 3, 4])

Documentation

Comprehensive tutorials, guides, API references, and the underlying mathematical foundations are available at katharos.readthedocs.io.

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