CODEWITHSUNDEEP
pythonpython-decorators
massi
massi

Reputation: 200

Python: how to sum/multiply an int with the value of a @property

The name property stands in the way here, so my searches has been unsuccessful. What I want to accomplice is multiply (sum , subtract, ...) an integer value to a value coming from a property (meaning @property):

class A:
    __att = 3
    @property
    def att():
        return __att
    
    def test_method(self):
        return 3*A.att
        
a = A()
x = a.test_method()

but I get TypeError: unsupported operand type(s) for *: 'int' and 'property'

I understand the meaning of the message: it's sort of trying to multiply an int to a method name instead of its result, but for properties, shouldn't it be transparent? I do not understand what I'm missing here.

Upvotes: 1

Views: 128

Answers (2)

wim
wim

Reputation: 363304

If you want a class property, you can stack decorators in Python < 3.13.

class A:
    __att = 3
    @classmethod
    @property
    def att(cls):
        return cls.__att

    def test_method(self):
        return 3*A.att

The value is accessible from a.att or A.att and shared between all instances. The "real" class attribute which the property gets is name-mangled at A._A__att.

Upvotes: 2

mipadi
mipadi

Reputation: 411122

You're calling the att attribute of the class (A.att):

return 3*A.att

As a class attribute, att is indeed a property.

You should call att using the instance (via self):

return 3*self.att

This is tangential to your question, but att also needs to take a self argument:

@property
def att(self):
    return self.__att

Upvotes: 2

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