Python Classes Best Practices

Question

I wonder if while working with OPP/Classes/Instances in Python I should be always using getAttr()/setAttr() when reading-writing from-to a Class's attribute/variable. Or dealing with the variable/attribute directly (such as self.my_attr = "some_value") would be a better practice?

Direct access to Class attr

class MyClass(object):
    def __init__(self):
        super(MyClass, self).__init__()
        self.my_attr = 'My_Value'

    def doSomething(self):
        localVariable = self.my_attr
        print localVariable

Using a Class's method to access a Class's attr

class MyClass(object):
    def __init__(self):
        super(MyClass, self).__init__()
        self.my_attr = 'My_Value'

    def getMyAttr(self):
        return self.my_attr

    def doSomething(self):
        localVariable = self.my_attr
        print localVariable

EDITED LATER:

While reading 'The Object-Oriented Thought Process' book (Matt Weisfeld : Developer's Library) ... The author states continuously throughout it:

"...Access to attributes within an object should be controlled by the object itself—no other object should directly change an attribute of another..."

"...If you control the access to the attribute, when a problem arises, you do not have to worry about tracking down every piece of code that might have changed the attribute—it can only be changed in one place (the setter)..."

I will be sticking to setters and getters then. Suggested/mentioned here Python's @property and @.setter make it even easier.

Concerning your edit: Other peoples' thought are generally not be adopted without reflection. Only because it is printed in a book, a fact doesn't become true. "Best" practices are only "best" for a given value of "best" and a given value of "practices". Putting every wee bit into setters and getters leads to Java's getter-setter-hell (I feel any Java code is 90% boiler plate code), having trust that "we are all adults here" (as the zen of python suggests) might be even worse. Maybe the truth is somewhere out there, between the two extrema. — Hyperboreus
– Hyperboreus, Commented Feb 10, 2014 at 1:11

Daniel Roseman · Accepted Answer · 2014-02-05 17:58:19Z

12

You should access the variable directly.

If you subsequently need to add some logic for getting/setting the value, convert it to a property.

answered Feb 5, 2014 at 17:58

Daniel Roseman

602k68 gold badges910 silver badges923 bronze badges

Sign up to request clarification or add additional context in comments.

Comments

Matt · Accepted Answer · 2016-02-17 01:03:13Z

10

Instead of the latter example, consider using the @property decorator.

class MyClass(object):
    def __init__(self):
        super(MyClass, self).__init__()
        self.__my_attr = 'My_Value'

    @property
    def my_attr(self):
        return self.__my_attr

    def doSomething(self):
        localVariable = self.__my_attr
        print localVariable

Use it only if you have good reason to protect the member, e.g. if you want to validate its values:

class Person:
    @property
    def age(self): return self.__age

    @age.setter
    def age(self, value):
        if value < 0: raise Exception('Age out of bounds.')
        self.__age = value

p = Person ()
p.age = 14
print (p.age)
p.age = -34

edited Feb 17, 2016 at 1:03

Matt

33 bronze badges

answered Feb 5, 2014 at 17:58

Hyperboreus

32.5k9 gold badges50 silver badges88 bronze badges

Collectives™ on Stack Overflow

Python Classes Best Practices

Direct access to Class attr

Using a Class's method to access a Class's attr

EDITED LATER:

2 Answers 2

Comments

Comments

Your Answer

Hot Network Questions

Collectives™ on Stack Overflow

Direct access to Class attr

Using a Class's method to access a Class's attr

EDITED LATER:

2 Answers 2

Comments

Comments

Your Answer

Sign up or log in

Post as a guest

Related