我有一个带有两个类方法的类(使用classmethod()函数),用于获取和设置本质上是静态变量的类。我尝试使用property()函数来处理这些,但它会导致错误。我能够在解释器中重现以下错误:
class Foo(object):
_var = 5
@classmethod
def getvar(cls):
return cls._var
@classmethod
def setvar(cls, value):
cls._var = value
var = property(getvar, setvar)
我可以演示类方法,但它们不能作为属性:
>>> f = Foo()
>>> f.getvar()
5
>>> f.setvar(4)
>>> f.getvar()
4
>>> f.var
Traceback (most recent call last):
File "<stdin>", line 1, in ?
TypeError: 'classmethod' object is not callable
>>> f.var=5
Traceback (most recent call last):
File "<stdin>", line 1, in ?
TypeError: 'classmethod' object is not callable
是否可以使用属性()函数与@classmethod装饰函数?
尝试一下,它可以在不更改/添加大量现有代码的情况下完成工作。
>>> class foo(object):
... _var = 5
... def getvar(cls):
... return cls._var
... getvar = classmethod(getvar)
... def setvar(cls, value):
... cls._var = value
... setvar = classmethod(setvar)
... var = property(lambda self: self.getvar(), lambda self, val: self.setvar(val))
...
>>> f = foo()
>>> f.var
5
>>> f.var = 3
>>> f.var
3
属性函数需要两个可调用参数。给它们lambda包装器(它将实例作为第一个参数传递),一切都很好。
我找到了一个解决这个问题的简单方法。它是一个叫做classutilities的包(pip install classutilities),请参阅这里关于PyPi的文档。
考虑的例子:
import classutilities
class SomeClass(classutilities.ClassPropertiesMixin):
_some_variable = 8 # Some encapsulated class variable
@classutilities.classproperty
def some_variable(cls): # class property getter
return cls._some_variable
@some_variable.setter
def some_variable(cls, value): # class property setter
cls._some_variable = value
你可以在类级和实例级使用它:
# Getter on class level:
value = SomeClass.some_variable
print(value) # >>> 8
# Getter on instance level
inst = SomeClass()
value = inst.some_variable
print(value) # >>> 8
# Setter on class level:
new_value = 9
SomeClass.some_variable = new_value
print(SomeClass.some_variable) # >>> 9
print(SomeClass._some_variable) # >>> 9
# Setter on instance level
inst = SomeClass()
inst.some_variable = new_value
print(SomeClass.some_variable) # >>> 9
print(SomeClass._some_variable) # >>> 9
print(inst.some_variable) # >>> 9
print(inst._some_variable) # >>> 9
如您所见,它在所有情况下都能正常工作。