oop-ext 2.1.0

OOP Extensions is a set of utilities for object oriented programming not found on Python's standard library.

What is OOP Extensions ?

OOP Extensions is a set of utilities for object oriented programming which is missing on Python core libraries.

Usage

oop_ext brings a set of object oriented utilities, it supports the concept of interfaces, abstract/overridable methods and more. oop_ext carefully checks that implementations have the same method signatures as the interface it implements and raises exceptions otherwise.

Here’s a simple example showing some nice features:

from oop_ext.interface import Interface, ImplementsInterface


class IDisposable(Interface):
    def dispose(self):
        """
        Clears this object
        """

    def is_disposed(self) -> bool:
        """
        Returns True if the object has been cleared
        """


@ImplementsInterface(IDisposable)
class MyObject(Disposable):
    def __init__(self):
        super().__init__()
        self._data = [0] * 100
        self._is_disposed = False

    def is_disposed(self) -> bool:
        return self._is_disposed

    def dispose(self):
        self._is_disposed = True
        self._data = []

If any of the two methods in MyObject are not implemented or have differ signatures than the ones declared in IDisposable, the ImplementsInterface decorator will raise an error during import.

Arbitrary objects can be verified if they implement a certain interface by using IsImplementation:

from oop_ext.interface import IsImplementation

my_object = MyObject()
if IsImplementation(my_object, IDisposable):
    # my_object is guaranteed to implement IDisposable completely
    my_object.dispose()

Alternatively you can assert that an object implements the desired interface with AssertImplements:

from oop_ext.interface import AssertImplements

my_object = MyObject()
AssertImplements(my_object, IDisposable)
my_object.dispose()

Type Checking

As of 1.1.0, oop-ext includes inline type annotations and exposes them to user programs.

If you are running a type checker such as mypy on your tests, you may start noticing type errors indicating incorrect usage. If you run into an error that you believe to be incorrect, please let us know in an issue.

The types were developed against mypy version 0.800.

See the docs for more information.

Contributing

For guidance on setting up a development environment and how to make a contribution to oop_ext, see the contributing guidelines.

Release

A reminder for the maintainers on how to make a new release.

Note that the VERSION should follow the semantic versioning as X.Y.Z Ex.: v1.0.5

1. Create a release-VERSION branch from upstream/master.

2. Update CHANGELOG.rst.

3. Push a branch with the changes.

4. Once all builds pass, push a VERSION tag to upstream.

5. Merge the PR.

2.1.0 (2021-03-19)

• #48: New type-checker friendly proxy = GetProxy(I, obj) function as an alternative to proxy = I(obj). The latter is not accepted by type checkers in general because interfaces are protocols, which can’t be instantiated.

  Also fixed a type-checking error with AsssertImplements:

  Only concrete class can be given where "Type[Interface]" is expected

  This happens due to python/mypy#5374.

2.0.0 (2021-03-10)

• #47: Interfaces no longer check type annotations at all.

  It was supported initially, but in practice this feature has shown up to be an impediment to adopting type annotations incrementally, as it discourages adding type annotations to improve existing interfaces, or annotating existing implementations without having to update the interface (and all other implementations by consequence).

  It was decided to let the static type checker correctly deal with matching type annotations, as it can do so more accurately than oop-ext did before.

1.2.0 (2021-03-09)

• #43: Fix support for type annotated Attribute and ReadOnlyAttribute:

  class IFoo(Interface):
      value: int = Attribute(int)

1.1.2 (2021-02-23)

• #41: Fix regression introduced in 1.1.0 where installing a callback using callback.After or callback.Before would make a method no longer compliant with the signature required by its interface.

1.1.1 (2021-02-23)

• #38: Reintroduce extra_args argument to Callback._GetKey, so subclasses can make use of it.

• #36: Fix regression introduced in 1.1.0 where Abstract and Implements decorators could no longer be used in interfaces implementations.

1.1.0 (2021-02-19)

• #25: oop-ext now includes inline type annotations and exposes them to user programs.

  If you are running a type checker such as mypy on your tests, you may start noticing type errors indicating incorrect usage. If you run into an error that you believe to be incorrect, please let us know in an issue.

  The types were developed against mypy version 0.800.

• #26: New type-checked Callback variants, Callback0, Callback1, Callback2, etc, providing type checking for all operations(calling, Register, etc) at nearly zero runtime cost.

  Example:

  from oop_ext.foundation.callback import Callback2
  
  
  def changed(x: int, v: float) -> None:
      ...
  
  
  on_changed = Callback2[int, float]()
  on_changed(10, 5.25)

• Fixed Callbacks.Before and Callbacks.After signatures: previously their signature conveyed that they supported multiple callbacks, but it was a mistake which would break callers because every parameter after the 2nd would be considered the sender_as_parameter parameter, which was forwarded to After and Before functions of the _shortcuts.py module.

1.0.0 (2020-10-01)

• Callbacks can be used as context manager, which provides a Register(callback, function), which automatically unregisters all functions when the context manager ends.

• Callback.Register(function) now returns an object with a Unregister() method, which can be used to undo the register call.

0.6.0 (2020-01-31)

• Change back the default value of requires_declaration to True and fix an error (#22) where the cache wasn’t properly cleared.

0.5.1 (2019-12-20)

• Fixes an issue (#20) where mocked classmethods weren’t considered a valid method during internal checks.

0.5.0 (2019-12-12)

• Add optional argument requires_declaration so users can decide whether or not @ImplementsInterface declarations are necessary.

0.4.0 (2019-12-03)

• Implementations no longer need to explicitly declare that they declare an interface with @ImplementsInterface: the check is done implicitly (and cached) by AssertImplements and equivalent functions.

0.3.2 (2019-08-22)

• Interface and implementation methods can no longer contain mutable defaults, as this is considered a bad practice in general.

• Null instances are now hashable.

0.3.1 (2019-08-16)

• Fix mismatching signatures when creating “interface stubs” for instances:

  foo = IFoo(Foo())

0.3.0 (2019-08-08)

• Interfaces now support keyword-only arguments.

0.2.4 (2019-03-22)

• Remove FunctionNotRegisteredError exception, which has not been in use for a few years.

0.2.3 (2019-03-22)

• Fix issues of ignored exception on nested callback.

0.2.1 (2019-03-14)

• Fix issues and remove obsolete code.

0.1.8 (2019-03-12)

• First release on PyPI.