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?
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
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)
其他回答
Hear是最简单的,可以在Jython下使用Java类:
class MyClass(SomeJavaClass):
def __init__(self):
setattr(self, "name_of_method_to_override", __method_override__)
def __method_override__(self, some_args):
some_thing_to_do()
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
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。
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!!!!!!!