result

What it is and what it does

Result is a type-safe container for representing success or failure outcomes without relying on exceptions. It provides Ok and Err classes that wrap values, letting you encode success or error states directly in function return types. The package is inspired by Rust's Result enum and fully type-annotated, making it compatible with MyPy and other type checkers for compile-time safety.

You use it by returning Ok(value) for success or Err(error) for failure, then checking the result with isinstance, is_ok/is_err functions, or Python 3.10+ match statements. It includes utility methods like map, unwrap, expect, and unwrap_or to transform and extract values. The design encourages explicit error handling at call sites rather than implicit exception propagation, making error paths visible in code.

Use it for

• Building APIs or functions where error cases are part of the normal control flow and should be handled explicitly rather than caught.
• Type-checking error handling with MyPy by narrowing result types through isinstance checks to ensure all branches are covered.
• Replacing tuple-based error returns (like returning (value, error_msg)) with a clearer, type-safe Result[T, E] signature.
• Chaining operations on results using map and map_err to transform values or errors without nested conditionals.
• Porting Rust code to Python while preserving the Result pattern for consistency and familiar error semantics.

Worth the install?

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Install

result on PyPI

Before you install

Low install friction with a single lightweight dependency (typing-extensions). Repository is archived and maintenance is abandoned as of 803 days since last release, though the package remains stable and widely used.

License in practice

MIT license permits unrestricted use, modification, and distribution with minimal restrictions—suitable for both open-source and commercial projects.

Quickstart

pip install result

from result import Ok, Err, Result

def divide(a: int, b: int) -> Result[int, str]:
    if b == 0:
        return Err("Cannot divide by zero")
    return Ok(a // b)

result = divide(10, 2)
if isinstance(result, Ok):
    print(result.ok_value)  # 5
else:
    print(result.err_value)

Package facts

Evidence: result-0.17.0-py3-none-any.whl

Tags

More Software Development packages

See also setuptools-rust · regress · msgfy · python-status · pyre-extensions · better-exceptions · cargo-lambda · numerary · infinity · tree-sitter-rust