如果我重写抽象属性方法,但忘记指定它仍然是子类中的属性方法,我希望Python解释器对我大喊大叫。
class Parent(metaclass=ABCMeta):
@property
@abstractmethod
def name(self) -> str:
pass
class Child(Parent):
@property # If I forget this, I want Python to yell at me.
def name(self) -> str:
return 'The Name'
if __name__ == '__main__':
print(Child().name)
Python真的没有内置的方法来做到这一点吗?我真的必须创建自己的装饰器来处理这种类型的行为吗?
您可以使用metaclass
:
class Parent(type):
def __new__(cls, name, bases, body):
if 'name' not in body.keys() or body['name'].__class__.__name__ != 'property':
raise TypeError(f"Can't instantiate class {name} without property name")
return super().__new__(cls, name, bases, body)
class Child(metaclass=Parent):
@property # If I forget this, raise TypeError
def name(self) -> str: # also, name must be implemented
return 'The Name'
if __name__ == '__main__':
print(Child().name)
当@property
被注释掉时,这会引发一个TypeError: Can't instantiate class Child without property name
!
您可以在Parent的__init__
方法中进行运行时检查,如果name
是一个方法,则引发异常。
class Parent(metaclass=ABCMeta):
def __init__(self):
assert not callable(self.name)
@abstractmethod
def name(self) -> str:
pass
class GoodChild(Parent):
@property
def name(self) -> str:
return 'The Name'
class BadChild(Parent):
def name(self) -> str:
return 'Whoops, not a property'
if __name__ == '__main__':
good_child = GoodChild()
print(good_child.name) # Prints 'The Name'
bad_child = BadChild() # Raises an AssertionError when initialized
TLDR-在我看来,不值得这么麻烦:
在linting/mypy和单元测试之间,应该涵盖你的大部分需求和类分析/元类的小技巧可能不值得它们带来额外的认知负荷;失败";你的装饰一次,但必须阅读异国情调的脚手架代码,你想做的每一次。
细节-实际用途被标记为什么
即if badchild1.name.startswith("John"):
将在运行时失败,例如,我希望mypy或pylint也在分析时标记,因为它将是一个方法对象。串联也是如此。唯一真正的监督候选者是f字符串、直接布尔值或==
、!=
相等比较,它们不在乎它不是字符串。
pylint有这样一句话:
test_171_prop.py:11 Method 'name' was expected to be 'property', found it instead as 'method' (invalid-overridden-method)
mypy没有任何问题。
然而,如果我加上这个:
child = Child()
print("name:" + child.name)
然后mypy说:
test_171_prop.py:16: error: Unsupported operand types for + ("str" and "Callable[[], str]")
Found 1 error in 1 file (checked 1 source file)
运行带有两行新行的代码会显示:
TypeError: can only concatenate str (not "method") to str