Metadata-Version: 1.2
Name: implements
Version: 0.1.5
Summary: pythonic interfaces
Home-page: http://implements.readthedocs.io
Author: Kamil Sindi
Author-email: ksindi@ksindi.com
Maintainer: Kamil Sindi
Maintainer-email: ksindi@ksindi.com
License: MIT
Description: Implements
        ==========
        
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        *Pythonic interfaces using decorators*
        
        Install
        -------
        
        Implements is available on PyPI and can be installed with `pip <https://pip.pypa.io>`_::
        
            pip install implements
            
        Note Python 3.5+ is required as it relies on new features of `inspect` module.
        
        Advantages
        ----------
        
        1. `Favor composition over inheritance <https://en.wikipedia.org/wiki/Composition_over_inheritance>`_.
        
        2. Inheriting from multiple classes can be problematic, especially when the superclasses have the same method name but different signatures. Implements will throw a descriptive error if that happens to ensure integrity of contracts.
        
        3. The decorators are evaluated at import time. Any errors will be raised then and not when an object is instantiated or a method is called.
        
        4. It's cleaner. Using decorators makes it clear we want share behavior. Also, arguments are not allowed to be renamed.
        
        5. Codebase is tiny: you can just copy the file over. This repo exists more for test coverage.
        
        Usage
        -----
        
        .. code-block:: python
        
            from implements import Interface, implements
        
        
            class Duck:
                def __init__(self, age):
                    self.age = age
        
        
            class Flyable(Interface):
                @staticmethod
                def migrate(direction):
                    pass
        
                def fly(self) -> str:
                    pass
        
        
            class Quackable(Interface):
                def fly(self) -> bool:
                    pass
        
                def quack(self):
                    pass
        
        
            @implements(Flyable)
            @implements(Quackable)
            class MallardDuck(Duck):
                def __init__(self, age):
                    super(MallardDuck, self).__init__(age)
        
                def migrate(self, dir):
                    return True
        
                def fly(self):
                    pass
        
        
        The above would throw the following errors:
        
        .. code-block:: python
        
            NotImplementedError: 'MallardDuck' must implement method 'fly((self) -> bool)' defined in interface 'Quackable'
            NotImplementedError: 'MallardDuck' must implement method 'quack((self))' defined in interface 'Quackable'
            NotImplementedError: 'MallardDuck' must implement method 'migrate((direction))' defined in interface 'Flyable'
        
        You can find a more detailed example in ``example.py`` and by looking at ``tests.py``.
        
        Justification
        -------------
        
        There are currently two idiomatic ways to rewrite the above example.
        
        The first way is to write base classes with mixins raising ``NotImplementedError`` in each method.
        
        .. code-block:: python
        
            class Duck:
                def __init__(self, age):
                    self.age = age
        
        
            class Flyable:
                @staticmethod
                def migrate(direction):
                    raise NotImplementedError("Flyable is an abstract class")
        
                def fly(self) -> str:
                    raise NotImplementedError("Flyable is an abstract class")
        
        
            class Quackable:
                def fly(self) -> bool:
                    raise NotImplementedError("Quackable is an abstract class")
        
                def quack(self):
                    raise NotImplementedError("Quackable is an abstract class")
        
        
            class MallardDuck(Duck, Quackable, Flyable):
        
                def __init__(self, age):
                    super(MallardDuck, self).__init__(age)
        
                def migrate(self, dir):
                    return True
        
                def fly(self):
                    pass
        
        But there are a couple drawbacks implementing it this way:
        
        1. We would only get a ``NotImplementedError`` when calling ``quack`` which can happen much later during runtime. Also, raising ``NotImplementedError`` everywhere looks clunky.
        
        2. It's unclear without checking each parent class where super is being called.
        
        3. Similarly the return types of ``fly`` in ``Flyable`` and ``Quackable`` are different. Someone unfamiliar with Python would have to read up on `Method Resolution Order <https://www.python.org/download/releases/2.3/mro/>`_.
        
        4. The writer of ``MallardDuck`` made method ``migrate`` an instance method and renamed the argument to ``dir`` which is confusing.
        
        5. We really want to be differentiating between behavior and inheritance.
        
        The advantage of using implements is it looks cleaner and you would get errors at import time instead of when the method is actually called.
        
        Another way is to use abstract base classes from the built-in ``abc`` module:
        
        .. code-block:: python
        
            from abc import ABCMeta, abstractmethod, abstractstaticmethod
        
        
            class Duck(metaclass=ABCMeta):
                def __init__(self, age):
                    self.age = age
        
        
            class Flyable(metaclass=ABCMeta):
                @abstractstaticmethod
                def migrate(direction):
                    pass
        
                @abstractmethod
                def fly(self) -> str:
                    pass
        
        
            class Quackable(metaclass=ABCMeta):
                @abstractmethod
                def fly(self) -> bool:
                    pass
        
                @abstractmethod
                def quack(self):
                    pass
        
        
            class MallardDuck(Duck, Quackable, Flyable):
                def __init__(self, age):
                    super(MallardDuck, self).__init__(age)
        
                def migrate(self, dir):
                    return True
        
                def fly(self):
                    pass
        
        
        Using abstract base classes has the advantage of throwing an error earlier
        on instantiation if a method is not implemented; also, there are static analysis
        tools that warn if two methods have different signatures. But it doesn't solve
        issues 2-4 and implements will throw an error even earlier in import.
        It also in my opinion doesn't look pythonic.
        
        Credit
        ------
        
        Implementation was inspired by a `PR <https://github.com/pmatiello/python-interface/pull/1/files>`_ of @elifiner.
        
        Test
        ----
        
        Running unit tests::
        
            make test
        
        Running linter::
        
            make lint
        
        Running tox::
        
            make test-all
        
        License
        -------
        
        MIT
        
Keywords: implements,interfaces
Platform: UNKNOWN
Classifier: Development Status :: 5 - Production/Stable
Classifier: Intended Audience :: Developers
Classifier: License :: OSI Approved :: MIT License
Classifier: Natural Language :: English
Classifier: Programming Language :: Python :: 3
Classifier: Programming Language :: Python :: 3.5
Classifier: Programming Language :: Python :: 3.6
