TypeError: object of type 'property' has no len()

May 7, 2023

I have this code of a class that contains a list _offers. For this list I created a property to allow access to it:

class OffersManager:    
    _offers: list[OfferData] = []
    
    @property
    def offers(cls) -> list[OfferData]:
        return cls._offers

The problem is that the program treats this list as a "property" object, so it gives me an error when I try to get the length of the list:

>>> len(OffersManager.offers)
>>> Traceback (most recent call last):
      File "<pyshell#1>", line 1, in <module>
        len(OffersManager.offers)
    TypeError: object of type 'property' has no len()

Can someone tell me the correct way to make a property return the attribute as a list?

>Solution :

You need to mark the property as a class method, so it’s bound to the class itself rather than the instances:

class OffersManager:    
    _offers: list[OfferData] = []
    
    @classmethod
    @property
    def offers(cls) -> list[OfferData]:
        return cls._offers