例如,在Java中,@Override注释不仅提供了重写的编译时检查,而且可以生成优秀的自文档代码。

我只是在寻找文档(尽管如果它是一些检查器(如pylint)的指示器,那是额外的奖励)。我可以在某处添加注释或文档字符串,但在Python中指示重写的惯用方法是什么?


当前回答

即兴对@mkorpela的伟大回答,这里有一个版本

更精确的检查、命名和引发的Error对象

def overrides(interface_class):
    """
    Function override annotation.
    Corollary to @abc.abstractmethod where the override is not of an
    abstractmethod.
    Modified from answer https://stackoverflow.com/a/8313042/471376
    """
    def confirm_override(method):
        if method.__name__ not in dir(interface_class):
            raise NotImplementedError('function "%s" is an @override but that'
                                      ' function is not implemented in base'
                                      ' class %s'
                                      % (method.__name__,
                                         interface_class)
                                      )

        def func():
            pass

        attr = getattr(interface_class, method.__name__)
        if type(attr) is not type(func):
            raise NotImplementedError('function "%s" is an @override'
                                      ' but that is implemented as type %s'
                                      ' in base class %s, expected implemented'
                                      ' type %s'
                                      % (method.__name__,
                                         type(attr),
                                         interface_class,
                                         type(func))
                                      )
        return method
    return confirm_override

下面是它在实践中的样子:

NotImplementedError未在基类中实现

class A(object):
    # ERROR: `a` is not a implemented!
    pass

class B(A):
    @overrides(A)
    def a(self):
        pass

会导致更具有描述性的NotImplementedError错误

function "a" is an @override but that function is not implemented in base class <class '__main__.A'>

完整的堆栈

Traceback (most recent call last):
  …
  File "C:/Users/user1/project.py", line 135, in <module>
    class B(A):
  File "C:/Users/user1/project.py", line 136, in B
    @overrides(A)
  File "C:/Users/user1/project.py", line 110, in confirm_override
    interface_class)
NotImplementedError: function "a" is an @override but that function is not implemented in base class <class '__main__.A'>

NotImplementedError“期望实现的类型”

class A(object):
    # ERROR: `a` is not a function!
    a = ''

class B(A):
    @overrides(A)
    def a(self):
        pass

会导致更具有描述性的NotImplementedError错误

function "a" is an @override but that is implemented as type <class 'str'> in base class <class '__main__.A'>, expected implemented type <class 'function'>

完整的堆栈

Traceback (most recent call last):
  …
  File "C:/Users/user1/project.py", line 135, in <module>
    class B(A):
  File "C:/Users/user1/project.py", line 136, in B
    @overrides(A)
  File "C:/Users/user1/project.py", line 125, in confirm_override
    type(func))
NotImplementedError: function "a" is an @override but that is implemented as type <class 'str'> in base class <class '__main__.A'>, expected implemented type <class 'function'>


@mkorpela answer的伟大之处在于检查发生在初始化阶段。检查不需要“运行”。参考前面的例子,类B从未初始化(B()),但NotImplementedError仍然会引发。这意味着可以更快地捕获覆盖错误。

其他回答

基于这个和fwc:s的答案,我创建了一个pip可安装包https://github.com/mkorpela/overrides

我经常在这里看到这个问题。 这主要发生在(再次)在我们的代码库中看到相同的错误之后:有人在重命名“接口”中的方法时忘记了一些“接口”实现类。

好吧,Python不是Java,但Python有强大的功能——显式比隐式好——在现实世界中,有一些真实的具体案例,这个东西会帮助我。

这是overrides decorator的草图。这将检查作为参数给出的类是否与被修饰的方法具有相同的方法(或其他东西)名称。

如果你能想到一个更好的解决方案,请张贴在这里!

def overrides(interface_class):
    def overrider(method):
        assert(method.__name__ in dir(interface_class))
        return method
    return overrider

其工作原理如下:

class MySuperInterface(object):
    def my_method(self):
        print 'hello world!'


class ConcreteImplementer(MySuperInterface):
    @overrides(MySuperInterface)
    def my_method(self):
        print 'hello kitty!'

如果你做了一个错误的版本,它会在类加载时引发一个断言错误:

class ConcreteFaultyImplementer(MySuperInterface):
    @overrides(MySuperInterface)
    def your_method(self):
        print 'bye bye!'

>> AssertionError!!!!!!!

您可以使用来自PEP 544的协议。使用这种方法,接口实现关系只在使用站点声明。

假设您已经有了一个实现(让我们称之为MyFoobar),您定义了一个接口(一个协议),它具有实现的所有方法和字段的签名,我们称之为IFoobar。

Then, at the use site, you declare the implementation instance binding to have the interface type e.g. myFoobar: IFoobar = MyFoobar(). Now, if you use a field/method that is missing in the interface, Mypy will complain at the use site (even if it would work at runtime!). If you failed to implement a method from the interface in the implementation, Mypy will also complain. Mypy won't complain if you implement something that doesn't exist in the interface. But that case is rare, since the interface definition is compact and easy to review. You wouldn't be able to actually use that code, since Mypy would complain.

现在,这还不包括在父类和实现类中都有实现的情况,比如ABC的一些使用。但是在Java中使用override,即使在接口中没有实现。这个解决方案适用于这种情况。

from typing import Protocol

class A(Protocol):
    def b(self):
        ...
    def d(self):  # we forgot to implement this in C
        ...

class C:
    def b(self):
        return 0

bob: A = C()

输入检查结果:

test.py:13: error: Incompatible types in assignment (expression has type "C", variable has type "A")
test.py:13: note: 'C' is missing following 'A' protocol member:
test.py:13: note:     d
Found 1 error in 1 file (checked 1 source file)

Python不是Java。当然,没有真正的编译时检查。

我认为文档字符串中的注释就足够了。这允许您的方法的任何用户输入help(obj.method),并看到该方法是一个覆盖。

你也可以用类Foo(interface)显式地扩展一个接口,这将允许用户输入help(interface .method)来了解你的方法想要提供的功能。

就像其他人说的,不像Java,没有@Overide标签,但是上面你可以使用装饰器创建自己的,但是我建议使用getattrib()全局方法,而不是使用内部dict,这样你就会得到如下内容:

def Override(superClass):
    def method(func)
        getattr(superClass,method.__name__)
    return method

如果你想,你可以在你自己的try catch中捕获getattr(),但我认为getattr方法在这种情况下更好。

此外,它还捕获绑定到类的所有项,包括类方法和变量

即兴对@mkorpela的伟大回答,这里有一个版本

更精确的检查、命名和引发的Error对象

def overrides(interface_class):
    """
    Function override annotation.
    Corollary to @abc.abstractmethod where the override is not of an
    abstractmethod.
    Modified from answer https://stackoverflow.com/a/8313042/471376
    """
    def confirm_override(method):
        if method.__name__ not in dir(interface_class):
            raise NotImplementedError('function "%s" is an @override but that'
                                      ' function is not implemented in base'
                                      ' class %s'
                                      % (method.__name__,
                                         interface_class)
                                      )

        def func():
            pass

        attr = getattr(interface_class, method.__name__)
        if type(attr) is not type(func):
            raise NotImplementedError('function "%s" is an @override'
                                      ' but that is implemented as type %s'
                                      ' in base class %s, expected implemented'
                                      ' type %s'
                                      % (method.__name__,
                                         type(attr),
                                         interface_class,
                                         type(func))
                                      )
        return method
    return confirm_override

下面是它在实践中的样子:

NotImplementedError未在基类中实现

class A(object):
    # ERROR: `a` is not a implemented!
    pass

class B(A):
    @overrides(A)
    def a(self):
        pass

会导致更具有描述性的NotImplementedError错误

function "a" is an @override but that function is not implemented in base class <class '__main__.A'>

完整的堆栈

Traceback (most recent call last):
  …
  File "C:/Users/user1/project.py", line 135, in <module>
    class B(A):
  File "C:/Users/user1/project.py", line 136, in B
    @overrides(A)
  File "C:/Users/user1/project.py", line 110, in confirm_override
    interface_class)
NotImplementedError: function "a" is an @override but that function is not implemented in base class <class '__main__.A'>

NotImplementedError“期望实现的类型”

class A(object):
    # ERROR: `a` is not a function!
    a = ''

class B(A):
    @overrides(A)
    def a(self):
        pass

会导致更具有描述性的NotImplementedError错误

function "a" is an @override but that is implemented as type <class 'str'> in base class <class '__main__.A'>, expected implemented type <class 'function'>

完整的堆栈

Traceback (most recent call last):
  …
  File "C:/Users/user1/project.py", line 135, in <module>
    class B(A):
  File "C:/Users/user1/project.py", line 136, in B
    @overrides(A)
  File "C:/Users/user1/project.py", line 125, in confirm_override
    type(func))
NotImplementedError: function "a" is an @override but that is implemented as type <class 'str'> in base class <class '__main__.A'>, expected implemented type <class 'function'>


@mkorpela answer的伟大之处在于检查发生在初始化阶段。检查不需要“运行”。参考前面的例子,类B从未初始化(B()),但NotImplementedError仍然会引发。这意味着可以更快地捕获覆盖错误。