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

如果你只是为了文档的目的,你可以定义你自己的覆盖装饰器:

def override(f):
    return f


class MyClass (BaseClass):

    @override
    def method(self):
        pass

这实际上只是花瓶,除非你创建override(f)的方式实际上是检查重写。

但是,这是Python,为什么要写成Java呢?

其他回答

这里是一个没有注释的不同解决方案。

它有一个稍微不同的目标。其他建议的解决方案检查给定的方法是否实际覆盖了父方法,而这个解决方案检查是否所有的父方法都被覆盖了。

你不必引发AssertionError,但可以打印警告或在生产环境中通过检查__init__中的env并在检查之前返回它。

class Parent:

    def a():
        pass

    def b():
        pass

class Child(Overrides, Parent):

    def a()

    # raises an error, as b() is not overridden


class Overrides:

    def __init__(self):
        # collect all defined methods of all base-classes
        bases = [b for b in self.__class__.__bases__ if b != Overrides]
        required_methods = set()
        for base in bases:
            required_methods = required_methods.union(set([f for f in dir(base) if not f.startswith('_')]))
        
        # check for each method in each base class (in required_methods)
        # if the class, that inherits `Overrides` implements them all
        missing = []
        # me is the fully qualified name of the CLASS, which inherits 
        # `Overrides`
        me = self.__class__.__qualname__
        for required_method in required_methods:

            # The method can be either defined in the parent or the child 
            # class. To check it, we get a reference to the method via 
            # getattr
            try:
                found = getattr(self, required_method)
            except AttributeError:
                # this should not happen, as getattr returns the method in 
                # the parent class if it is not defined in the cild class.
                # It has to be in a parent class, as the required_methods 
                # is a union of all base-class methods.
                missing.append(required_method)
                continue
            
            # here is, where the magic happens.
            # found is a reference to a method, and found.__qualname__ is
            # the full-name of the METHOD. Remember, that me is the full
            # name of the class. 
            # We want to check, where the method is defined. If it is 
            # defined in an parent class, we did no override it, thus it 
            # is missing. 
            # If we did not override, the __qualname__ is Parent.method
            # If we did override it, the __qualname__ is Child.method
            # With this fact, we can determine if the class, which uses
            # `Override` did implement it.
            if not found.__qualname__.startswith(me + '.'):
                missing.append(required_method)

        # Maybe a warning would be enough here
        if missing != []:
            raise AssertionError(f'{me} did not override these methods: {missing}')

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。

下面是一个不需要指定interface_class名称的实现。

import inspect
import re

def overrides(method):
    # actually can't do this because a method is really just a function while inside a class def'n  
    #assert(inspect.ismethod(method))

    stack = inspect.stack()
    base_classes = re.search(r'class.+\((.+)\)\s*\:', stack[2][4][0]).group(1)

    # handle multiple inheritance
    base_classes = [s.strip() for s in base_classes.split(',')]
    if not base_classes:
        raise ValueError('overrides decorator: unable to determine base class') 

    # stack[0]=overrides, stack[1]=inside class def'n, stack[2]=outside class def'n
    derived_class_locals = stack[2][0].f_locals

    # replace each class name in base_classes with the actual class type
    for i, base_class in enumerate(base_classes):

        if '.' not in base_class:
            base_classes[i] = derived_class_locals[base_class]

        else:
            components = base_class.split('.')

            # obj is either a module or a class
            obj = derived_class_locals[components[0]]

            for c in components[1:]:
                assert(inspect.ismodule(obj) or inspect.isclass(obj))
                obj = getattr(obj, c)

            base_classes[i] = obj


    assert( any( hasattr(cls, method.__name__) for cls in base_classes ) )
    return method

在Python 2.6+和Python 3.2+中,你可以这样做(实际上是模拟的,Python不支持函数重载,子类会自动覆盖父类的方法)。我们可以使用decorator。但首先,请注意Python的@decorators和Java的@Annotations是完全不同的东西。前一个是带有具体代码的包装器,后一个是编译器的标志。

为此,首先执行pip安装multipledispatch

from multipledispatch import dispatch as Override
# using alias 'Override' just to give you some feel :)

class A:
    def foo(self):
        print('foo in A')

    # More methods here


class B(A):
    @Override()
    def foo(self):
        print('foo in B')
    
    @Override(int)
    def foo(self,a):
        print('foo in B; arg =',a)
        
    @Override(str,float)
    def foo(self,a,b):
        print('foo in B; arg =',(a,b))
        
a=A()
b=B()
a.foo()
b.foo()
b.foo(4)
b.foo('Wheee',3.14)

输出:

foo in A
foo in B
foo in B; arg = 4
foo in B; arg = ('Wheee', 3.14)

注意,这里必须使用带有括号的decorator

需要记住的一件事是,由于Python没有直接的函数重载,所以即使类B没有继承自类A,但需要所有这些foo,也需要使用@Override(尽管在这种情况下使用别名'Overload'会更好看)

我创建的装饰器不仅检查覆盖属性的名称是否为该属性所在类的任何超类(无需指定超类),还检查确保覆盖属性必须与被覆盖属性的类型相同。类方法被视为方法,静态方法被视为函数。这个装饰器适用于可调用对象、类方法、静态方法和属性。

源代码见:https://github.com/fireuser909/override

此装饰器仅适用于作为重写实例的类。OverridesMeta,但是如果你的类是一个自定义元类的实例,使用create_custom_overrides_meta函数来创建一个与覆盖装饰器兼容的元类。对于测试,运行覆盖。__init__模块。