Changelog

Changelog

All notable changes to this project will be documented in this file.

The format is based on Keep a Changelog, and this project adheres to Semantic Versioning.

Generally, more significant breaking changes will be put near the top of each category.

Documentation here: https://py-maybetype.readthedocs.io/en/latest/reference/

[0.12.0] - 2026-05-16

Added

• Added Warning categories to errors:

  • MaybeInstanceWarning: Emitted when creating a Maybe object directly

  • ResultInstanceWarning: Emitted when creating a Result object directly

  • NothingTypeInitWarning: Emitted when calling NothingType.__init__() for a second time instead of using Nothing

Changed

• Result is no longer hashable, but is still comparable

  • Instead of comparing the hash of a tuple of the class and wrapped value, False is returned if the compared objects are not of the same type, otherwise their wrapped values are compared

• Any warnings emitted now have a proper category assigned to them instead of only a message

Removed

• Removed __hash__ method from Result

[0.11.0] - 2026-04-06

Added

• Added classes Result, Ok, and Err to mimic the behavior of Rust’s Result type

  • See docs for all introduced methods: https://py-maybetype.readthedocs.io/en/latest/reference/index.html#maybetype.Result

• Added the errors module

  • Added exception ResultUnwrapError

• Added test module test_result

Changed

• Changed docstring of function maybe to describe the predicate parameter more succinctly

• Updated test test_maybe.test_maybe_with_predicate_and_filter to ensure maybe(val).filter(predicate) is equivalent to maybe(val, predicate)

• Instancing NothingType more than once now emits a warning suggesting the use of the Nothing singleton

[0.10.1] - 2026-03-22

Fixed

• Fixed .gitignore rule mistakenly excluding maybetype/__init__.py, thus rendering the package effectively empty

[0.10.0] - 2026-03-21

Added

• Added method Maybe.cast

  • Casts the type of the wrapped value: maybe(...).cast(int) → Maybe[int]

• Added method Maybe.flatten

  • Replicates Rust’s Option::flatten

• Added method Maybe.inspect

  • Replicates Rust’s Option::inspect

• Added method Maybe.reduce

  • Replicates Rust’s Option::reduce

• Added method Maybe.replace

  • Replicates Rust’s Option::replace

• Added method Maybe.unwrap_or_else

  • Replicates Rust’s Option::unwrap_or_else

• Added method Maybe.unzip

  • Replicates Rust’s Option::unzip

• Added method Maybe.xor

  • Replicates Rust’s Option::xor

• Added method Maybe.zip

  • Replicates Rust’s Option::zip

• Added test test_maybe.test_maybe_cast

• Added test test_maybe.test_maybe_flatten

• Added test test_maybe.test_maybe_inspect

• Added test test_maybe.test_maybe_reduce

• Added test test_maybe.test_maybe_replace

• Added test test_maybe.test_maybe_unwrap_or_else

• Added test test_maybe.test_maybe_unzip

• Added test test_maybe.test_maybe_xor

• Added test test_maybe.test_maybe_zip

Changed

• Renamed attribute Maybe.val to Maybe._val, should now be treated as a private attribute

• Method Maybe.and_then parameter func now must return Maybe, making it more like Option::and_then

• Method Maybe.map is no longer a static method and is now more in line with Option::map in functionality

  • The previous behavior of Maybe.map is largely unnecessary as it would produce the exact same result as calling Maybe.cat with a regular map() object

• Method Maybe.attr now optionally takes a default parameter

• Method Maybe.unwrap parameter exc now defaults to a string instead of None, and no longer accepts None

• Renamed class _Nothing to NothingType

  • The class was marked as private to encourage use of the Nothing singleton instead, but since one could want to use the class for type annotations, and the singleton can’t be used for annotations, it was renamed to both make it no longer private and clarify that it is the type

• Renamed method Maybe.test to Maybe.filter

  • The docstring for Maybe.filter has also been rewritten a bit to be more concise

• A number of tests changed in test_maybe:

  • test_maybe_and_then rewritten to test for its new functionality

  • test_maybe_map rewritten to test for its new functionality

  • test_maybe_then rewritten to be less verbose

  • Renamed test_maybe_with_predicate_and_test to test_maybe_with_predicate_and_filter

Removed

• Removed method Maybe.attr_or

• Removed parameter err from method Maybe.attr

[0.9.0] - 2026-03-15

Added

• Added method Maybe.bind

  • Largely the same as Haskell’s >>=, x.bind(f) is essentially the same as x >>= f

• Added test test_maybe.test_bind

Changed

• Added from __future__ import annotations import to maybetype/__init__.py for unquoted forward references

• Added type annotation to Maybe.val in Maybe.__init__ to give more specificity for ty

• Removed type variable from signature of _Nothing class as it’s never used

• Replaced # type: ignore directive in test test_maybe.test_nothing_instance_always_wraps_none with more specific # ty:ignore[invalid-argument-type] directive

• Expanded test test_maybe.test_equality slightly

Fixed

• Fixed incorrectly written test test_maybe.test_maybe_or

[0.8.0] - 2026-02-16

Added

• Added test test_maybe.test_unwrap_nothing_callback

Changed

• Updated a number of docstrings to fix errors or improve clarity

• Changed Maybe.unwrap() default error message to a more succinct “unwrapped Nothing”

• Method Maybe.unwrap() argument exc can now also be a string, in which case ValueError is raised with that string as its sole argument if the instance was Nothing

• Renamed multiple tests in module test_maybe:

  • test_maybe_none_unwrap_error → test_unwrap_nothing

  • test_maybe_unwrap_or → test_unwrap_or

  • test_maybe_pattern_matching → test_pattern_matching

• Renamed type variable R to U in signature of Maybe.and_then()

• exc argument of method Maybe.unwrap() now expects a function that takes no arguments

[0.7.0] - 2026-02-05

Added

• Added static method Maybe.sequence()

• Added methods to Maybe:

  • and_then(): Similar to Maybe.then(), but returns a Maybe instance

  • test(): Returns Some if the instance is Some and the test function returns True when called with the wrapped value, otherwise returns Nothing

Changed

• Renamed static method Maybe.int() to Maybe.try_int()

• Maybe.__hash__() now returns hash() called with the wrapped value instead of accessing its __hash__() method

• Most type signatures now use the more standard type variable naming of T, U, V…

  • The only exception currently is the static method Maybe.map(), which uses A and B since T already belongs the Maybe class’ scope and the method operates on unrelated types

Removed

• Removed method Maybe.this_or()

  • Redundant, maybe(x).this_or(y) is exactly the same as maybe(x) or Some(y)

[0.6.0] - 2026-01-21

Changed

• Project string has been changed from "maybetype" to "py-maybetype" for getting metadata in const

[0.5.0] - 2026-01-18

Added

• Added __match_args__ attribute to Maybe to allow using its value in match/case pattern matching

• Added method Maybe.unwrap_or()

• Added classes Some and _Nothing

  • _Nothing is intended to be used through the Nothing singleton instance, rather than constructing new instances of it, since effectively all _Nothing instances should behave the same

  • Instances of Some are always truthy, and Nothing is always falsy

• Added function maybe()

  • Returns either a Some instance or the Nothing singleton depending on the given value and predicate, similar to the previous functionality of Maybe.__init__()

  • Usage should now replace direct instancing of Maybe

Changed

• Maybe.__init__() body moved to maybe() function, now simply assigns the passed val to its val attribute

  • A warning is now issued if Maybe’s constructor is called directly

• Replaced uses of NoReturn with Never

• Maybe.get() now directly checks for the __getitem__ method on the wrapped value instead of checking Sequence | Mapping

• Anywhere Maybe(None) would have been returned now returns the Nothing singleton

Fixed

• Maybe.attr_or() no longer has a default argument of None for its default parameter, as the docstring describes

[0.4.0] - 2026-01-02

Added

• Added module const

Changed

• Updated all docstrings to use reStructuredText markup for Sphinx docs generation

Fixed

• Fixed the example in Maybe.cat’s docstring incorrectly attempting to use .cat() on the list of Maybe objects, now correctly shows usage of Maybe.cat(vals)

[0.3.1] - 2025-12-31

Fixed

• Corrected the docstring of Maybe.__init__()’s description of the just_condition parameter, which incorrectly stated just_condition must return True for the constructor to return Maybe(None)—the opposite is true, Maybe(None) is returned if just_condition returns False

[0.3.0] - 2025-12-27

Added

• Added the just_condition argument to Maybe’s constructor, a function that takes the to-be-wrapped value as an argument, which allows defining a custom condition in which Maybe(None) will be returned if the function returns False

  • e.g. Maybe(0) == Maybe(0), however Maybe(0, lambda x: x > 0) == Maybe(None)

[0.2.0] - 2025-12-08

Added

• Added test module tests/test_maybe.py

[0.1.0] - 2025-12-07