In python, should attributes only be accessed by methods?

Question

Here are two examples of classes that handle their attribute differently.

class MyClassA():
    def __init__(self):
        self.my_attribute = 1

class MyClassB():
    def __init__(self):
        self._my_attribute = 1

    def get_my_attribute(self):
        return self._my_attribute

    def set_my_attribute(self, value):
        self._my_attribute = value

Is there a python consensus on which is best practice?

Answer 1

Best practice is to pick the one that meets your needs. If you need someone using your class to use the getter and setter - for example to perform checks, or to take care of required side-effects - then that's what you should do.

If it's just an attribute that you're happy to have changed by other code (no side-effects) the first solution is fine.

Note that there's also @property decorators for a nicer way to do the second type - which would be best practice over these get_... and set_... methods:

class MyClassB():
    def __init__(self):
        self._my_attribute = 1

    @property
    def my_attribute(self):
        return self._my_attribute

    @my_attribute.setter
    def my_attribute(self, value):
        self._my_attribute = value

Note that adding the _ doesn't actually hide the attribute, it just generates warnings in editors that respect it:

b = MyClassB()
print(b.my_attribute)
b.my_attribute = 10
print(b.my_attribute)
print(b._my_attribute)  # generates a warning, but works all the same

Output:

1
10
10