Errorz

Python officially handle errors using exceptions. This library provides a lightweight approach inspired by the Result type used in Rust and other functional programming languages: Result is an union between a success value and an error value.

The main advantage over exceptions is that they are expressed as values in the type system. This allows for better static guarantees and make code more explicit and easier to compose, since results are just like any other value that can be passed around and manipulated without cluncky try/catch blocks. Exceptions also break control flow and can be easily forgotten and lead to crashes and brittle refactorings.

The cannonical way to implement this pattern is to use a tagged union of Ok[T] and Err[E]. This is what Rust and Haskell do and there are some Python libraries that follow this approach, e.g., returns. However, Python don't have native tagged unions and using them often feels unergnomic and non-Pythonic. This library explores a more lightweight approach that defines Result[T, E] = T | Error[E], where Error[E] is a special abstract wrapper around an error value. This is simular to the approach we used in the optionz library for nullables, where it was more lightweight and in line with established Python idioms.

Installation

Install Errorz using pip/uv/poetry whatever you like. For example:

pip install errorz

Errorz consists of a single file, so you can also just copy the __init__.py file to your project as errorz.py and import it from there. Our special Error wrapper is defined as a protocol and has some special structure to ensure that different copies of the vendorized lib can coexist without conflicts.

Usage

Import err and use the functions as needed.

import errorz as rz

rz.unwrap(42) # 42
rz.unwrap(rz.err("error")) # raises ValueError

Documentation

The documentation is available at https://optionz.rtfd.io/ and includes more examples and explanations of the functions provided by the library.

License

Optionz is licensed under the MIT License. See LICENSE for more details.