result.py

A Python implementation inspired by Rust's Result<T, E>, representing operations that can either succeed (Ok) or fail (Err).

Installation

$ pip install pytresult

Key Features

• 100% Typed: Works flawlessly with mypy — zero type errors, guaranteed.

• Well Tested: Solid 100% test coverage with pytest so you can trust it.

• No Dependencies: Just install and go — nothing else required.

• Rust-Style: Clean, explicit error handling inspired by Rust’s Result.

Motivation

Using Result helps avoid excessive exception handling and promotes more explicit and robust error handling.

Usage Example

from result import Result, Ok, Err

def divide(a: int, b: int) -> Result[float, str]:
    if b == 0:
        return Err("division by zero")
    return Ok(a / b)

result = divide(10, 2)

if result.is_ok():
    print("Success:", result.unwrap())
else:
    print("Error:", result)  # or result.unwrap_or(0)

Patterns

if let Ok(...) { }

• Rust

  fn divide(a: i32, b: i32) -> Result<f32, String> {
      if b == 0 {
          Err("division by zero".to_string())
      } else {
          Ok(a as f32 / b as f32)
      }
  }
  
  let result = divide(10, 2);
  
  if let Ok(value) = result {
      println!("Success: {}", value);
  }
  

• Python

  from result import Result, Ok, Err
  
  def divide(a: int, b: int) -> Result[int, str]:
      if b == 0:
          return Err("division by zero")
      return Ok(a // b)
  
  result = divide(10, 2)
  
  if r := result.ok():
      assert r is not None
      assert r == 5
  

if let Err(...) { }

• Rust

  fn divide(a: i32, b: i32) -> Result<f32, String> {
      if b == 0 {
          Err("division by zero".to_string())
      } else {
          Ok(a as f32 / b as f32)
      }
  }
  
  let result = divide(10, 0);
  
  if let Err(error) = result {
      println!("Error: {}", error);
  }
  

• Python

  from result import Result, Ok, Err
  
  def divide(a: int, b: int) -> Result[int, str]:
      if b == 0:
          return Err("division by zero")
      return Ok(a // b)
  
  result = divide(10, 0)
  
  if e := result.err():
      assert e is not None
      assert e == "division by zero"
  

Testing

Tests are written using pytest.

To run the tests:

poetry run pytest