how to define IronPython static property?

Question

I have found previous discussing about defining Static Methods in (Iron)Python, however, I didn't find any about Static Properties. I assume you can definitively create Static Properties since properties are just methods for the .NET CLR and that's what I did in the code below, however, it looks like by calling the Static Property "StaticField" I cannot access the value of the Static Field "__staticField" it is linked to instead I get a reference where the property is stored? , but If I use the Static Method "getStaticField" that is used as the Get Property it does correctly give me the value "2".

So the question is: can you define Static Properties in (Iron)Python? and how can I use them to get the value and not the reference to the property method?

Thanks in advance.

class Test(object):
    __instanceField = 0
    __staticField = 0    

    # Instance Property (read-only)
    def getInstanceField(self):   
        return self.__instanceField    
    InstanceField = property(getInstanceField, None, None)

    # Static Property (read-only)
    @staticmethod
    def getStaticField():
        return Test.__staticField        
    StaticField = property(getStaticField, None, None)

    # Instance Method
    def instanceMethod(self, n):
        self.__instanceField += 1   
        print 'instanceMethod', n

    # Static Method
    @staticmethod
    def staticMethod(n):
        Test.__staticField += 1  
        print 'staticMethod', n

# Calling Static Methods
Test.staticMethod(5)
Test.staticMethod(10)

# Calling Instance Methods
t = Test()
t.instanceMethod(5)
t.instanceMethod(10)

print 'InstanceProperty', t.InstanceField 
#prints 2
print 'StaticProperty', Test.StaticField 
#prints: <property object at 0x000000000000002B>
print 'StaticPropertyMethod', Test.getStaticField()
#prints 2

I think I found what the problem "could" be... The problem seems to be that the StaticProperty = property(getStaticField, none, none) is getting the Getter parameter as an instance method, that's why when I call it later on it gives me the property object at 0x0000... The thing is that it doesn't allow me to assign a getter as Static: StaticField = property(Test.getStaticField, None, None) Error: global Test is not defined. — Carlos Quintanilla
– Carlos Quintanilla, Commented Jul 9, 2011 at 22:05

aknuds1 · Accepted Answer · 2014-04-29 10:29:51Z

1

this answer is for python in general, and not specific to IronPython.

property is a convenience for creating a descriptor, an object which supplies a __get__ and optionally __set__ and __del__ methods. The __get__ method accepts arguments for the target instance and also the associated class, but __set__ is never called for classes. If all you need is getter behavior without setter behavior, just implement a descriptor directly

class StaticGetter(object):
    def __init__(self, attr):
        self.attr = attr
    def __get__(self, instance, owner):
        # owner is the class, your getter code here
        return getattr(owner, attr)

class Test(object):
    __staticField = 0
    staticField = StaticGetter('_Test__staticField')

In the case of a setter, you could supply a __set__ method, which infers the class from the instance, but arranging for Test.staticField = newvalue to instead call Test.staticField.someSetterMethod(newvalue) will require a new metaclass.

edited Apr 29, 2014 at 10:29

aknuds1

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answered Jul 8, 2011 at 19:34

SingleNegationElimination

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2 Comments

Carlos Quintanilla Over a year ago

Thanks for your comment TokenMacGuy, interesting use of the getattr function (or __getattribute__()) but I do not want to define a separate class just to handle an static property if I can do the same using the getStaticField() method instead. The real question here is if I can define a static property as a syntax built-in support in (iron)python.

SingleNegationElimination Over a year ago

you could supply your own __getattribute__ method in a metaclass to do this, but that solution would be a bit more convloluted.

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