CODEWITHSUNDEEP
python
boatswain19
boatswain19

Reputation: 11

How does one prevent possible overwriting object attributes with illegal/illogical values?

I'm familiarizing myself with Python, and I have a question on rewriting attributes with illegal values.

Suppose I have a class Human, with attribute limbs, like so:

class Human:
    def __init__(self, limbs):
        if limbs > 4:
           raise ValueError('Humans dont have more than 4 limbs.')
        self.limbs = limbs

h1 = Human(5)       # Raises error - good.
h2 = Human(4)
h2.limbs = 5         # How do I protect against this?

Setting the limbs attribute to 5 would be caught via the constructor, but it is allowed via direct assignment. Is there a way to enforce error checking on attribute assignment? Should I be using an immutable string/tuple?

Again, I'm very new so I apologize if this is a silly question. Thanks!

Upvotes: 1

Views: 164

Answers (1)

kingkupps
kingkupps

Reputation: 3524

You could use the property decorator to make getters and setters for your property.

class Human(object):

    def __init__(self, limbs):
        self.limbs = limbs

    @property
    def limbs(self):
        return self._limbs

    @limbs.setter
    def limbs(self, new_value):
        if new_value > 4:
            raise ValueError("Humans don't have more than 4 limbs.")
        self._limbs = new_value

human = Human(4)
human.limbs = 5  # This will raise an exception

That said, if someone really wants to change this, they can still set self._limbs to whatever they want.

EDIT: Updated the example to use the setter in the constructor per @chepner's comment.

Upvotes: 4

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