接口支持Python 2.7和Python 3.4+。

要安装接口，你必须

pip install python-interface

示例代码:

from interface import implements, Interface

class MyInterface(Interface):

    def method1(self, x):
        pass

    def method2(self, x, y):
        pass


class MyClass(implements(MyInterface)):

    def method1(self, x):
        return x * 2

    def method2(self, x, y):
        return x + y

接口支持Python 2.7和Python 3.4+。

要安装接口，你必须

pip install python-interface

示例代码:

from interface import implements, Interface

class MyInterface(Interface):

    def method1(self, x):
        pass

    def method2(self, x, y):
        pass


class MyClass(implements(MyInterface)):

    def method1(self, x):
        return x * 2

    def method2(self, x, y):
        return x + y

在现代Python 3中，使用抽象基类实现接口要简单得多，它们的作用是作为插件扩展的接口契约。

创建接口/抽象基类:

from abc import ABC, abstractmethod

class AccountingSystem(ABC):

    @abstractmethod
    def create_purchase_invoice(self, purchase):
        pass

    @abstractmethod
    def create_sale_invoice(self, sale):
        log.debug('Creating sale invoice', sale)

创建一个普通的子类并覆盖所有抽象方法:

class GizmoAccountingSystem(AccountingSystem):

    def create_purchase_invoice(self, purchase):
        submit_to_gizmo_purchase_service(purchase)

    def create_sale_invoice(self, sale):
        super().create_sale_invoice(sale)
        submit_to_gizmo_sale_service(sale)

您可以选择在抽象方法(如create_sale_invoice())中使用通用实现，在上面的子类中使用super()显式调用它。

没有实现所有抽象方法的子类实例化失败:

class IncompleteAccountingSystem(AccountingSystem):
    pass

>>> accounting = IncompleteAccountingSystem()
Traceback (most recent call last):
  File "<stdin>", line 1, in <module>
TypeError: Can't instantiate abstract class IncompleteAccountingSystem with abstract methods
create_purchase_invoice, create_sale_invoice

通过将相应的注释与@abstractmethod组合，还可以拥有抽象属性、静态方法和类方法。

抽象基类对于实现基于插件的系统非常有用。类的所有导入子类都可以通过__subclasses__()访问，所以如果你用importlib.import_module()从插件目录加载所有类，如果它们是基类的子类，你可以通过__subclasses__()直接访问它们，并且你可以确保在实例化期间对所有类强制执行接口契约。

下面是上面AccountingSystem例子的插件加载实现:

...
from importlib import import_module

class AccountingSystem(ABC):

    ...
    _instance = None

    @classmethod
    def instance(cls):
        if not cls._instance:
            module_name = settings.ACCOUNTING_SYSTEM_MODULE_NAME
            import_module(module_name)
            subclasses = cls.__subclasses__()
            if len(subclasses) > 1:
                raise InvalidAccountingSystemError('More than one '
                        f'accounting module: {subclasses}')
            if not subclasses or module_name not in str(subclasses[0]):
                raise InvalidAccountingSystemError('Accounting module '
                        f'{module_name} does not exist or does not '
                        'subclass AccountingSystem')
            cls._instance = subclasses[0]()
        return cls._instance

然后你可以通过AccountingSystem类访问计费系统插件对象:

>>> accountingsystem = AccountingSystem.instance()

(灵感来自这篇pymotw3帖子。)

There are third-party implementations of interfaces for Python (most popular is Zope's, also used in Twisted), but more commonly Python coders prefer to use the richer concept known as an "Abstract Base Class" (ABC), which combines an interface with the possibility of having some implementation aspects there too. ABCs are particularly well supported in Python 2.6 and later, see the PEP, but even in earlier versions of Python they're normally seen as "the way to go" -- just define a class some of whose methods raise NotImplementedError so that subclasses will be on notice that they'd better override those methods!-)

类似这样的东西(可能不起作用，因为我周围没有Python):

class IInterface:
    def show(self): raise NotImplementedError

class MyClass(IInterface):
    def show(self): print "Hello World!"

对抽象基类使用abc模块似乎可以达到目的。

from abc import ABCMeta, abstractmethod

class IInterface:
    __metaclass__ = ABCMeta

    @classmethod
    def version(self): return "1.0"
    @abstractmethod
    def show(self): raise NotImplementedError

class MyServer(IInterface):
    def show(self):
        print 'Hello, World 2!'

class MyBadServer(object):
    def show(self):
        print 'Damn you, world!'


class MyClient(object):

    def __init__(self, server):
        if not isinstance(server, IInterface): raise Exception('Bad interface')
        if not IInterface.version() == '1.0': raise Exception('Bad revision')

        self._server = server


    def client_show(self):
        self._server.show()


# This call will fail with an exception
try:
    x = MyClient(MyBadServer)
except Exception as exc:
    print 'Failed as it should!'

# This will pass with glory
MyClient(MyServer()).client_show()