Will Price Posts About

Properties in python

As we all know, it’s important to wrap field access of an object in a function e.g. get_name simply returns self.name. In python one can consider this an antipattern since we have these wonderful things called properties.

properties allow you to add a getter (or setter) when you need one, rather than from the get go. Imagine you’d written a tonne of client code where you’re accessing a password of a user: e.g. user.password, but you’ve now decided that any time the user password is accessed it should be logged, you might be thinking “Oh god no, why didn’t I use a getter, I could have put the logging call inside of that”. Well no worries, you can transparently do this!

Go from this:

class User(object):
    def __init__(self, name, password):
        self.name = name
        self.password = password

To this:

class User(object):
    def __init__(self, name, password):
        self.name = name
        self._password = password

    @property
    def password(self):
        log("Password of user %s, was accessed" % self.name)
        return _password

Now any time someone calls user.password it’ll call the password function, log the password access and then return the property.