class Town:
     
    def __init__(self, name: str, country: str, population: int):

        #assert len(name) > 1, "The name of the town must be at least two characters long"
        self.name = name
        self.county = country
        self.population = population

    @property
    def name(self):
        return self.__name

    @name.setter
    def name(self,value):
        if len(value) < 2 or len(value) > 50:
            raise ValueError("The Name of the town must be between 2 and 50 characters")
        self.__name = value

For example I want to restrict the name attribute to be changed from the outside. Now it is possible with this name.setter. If i remove this setter it will work as I want but I will loose validations that I was made in the setter. What is the best way to keep aplying my validations for name attribute but not to be changed from the outside

CodePudding user response：

It sounds like you want to set the name once, and then make it immutable. So do exactly that in __init__ and remove the setter:

class Town:
    def __init__(self, name: str, country: str, population: int):
        if len(name) < 2 or len(name) > 50:
            raise ValueError("The Name of the town must be between 2 and 50 characters")

        self.__name = name
        self.county = country
        self.population = population

    @property
    def name(self):
        return self.__name

If you want it to be internally modifiable somehow, use a private method to set it:

class Town:
    def __init__(self, name: str, country: str, population: int):
        self.__set_name(name)
        self.county = country
        self.population = population

    def __set_name(self, value):
        if len(value) < 2 or len(value) > 50:
            raise ValueError("The Name of the town must be between 2 and 50 characters")
        self.__name = value

    @property
    def name(self):
        return self.__name