CODEWITHSUNDEEP
pythondjangopython-3.x
Lord Elrond
Lord Elrond

Reputation: 16002

Python What is the difference between calling "self.property" and creating a method that returns "self.property"?

Lets say I have a class like this:

class SomeClass:
    some_property = 'property'

    def get_some_property(self):
        return self.some_property

    def some_method(self):
        pass

What is difference (if any) between var1 and var2 in the following:

    def some_method(self):
        var1 = self.some_property
        var2 = self.get_some_property()

For a less abstract example of this question, consider the FormMixin class in django.generic.views.edit, which looks something like this:

class FormMixin(ContextMixin):
    """Provide a way to show and handle a form in a request."""
    initial = {}
    form_class = None
    success_url = None
    prefix = None

    ...

    def get_form_class(self):
        """Return the form class to use."""
        return self.form_class

    def get_form(self, form_class=None):
        """Return an instance of the form to be used in this view."""
        if form_class is None:
            form_class = self.get_form_class()
        return form_class(**self.get_form_kwargs())

The method get_form_class returns the form_class property of self, but isn't this exactly the same as calling self.form_class?

Upvotes: 1

Views: 101

Answers (1)

Barmar
Barmar

Reputation: 780798

Using functions makes it easy to have different classes with the same interface, but different implementations. Some implementations may store the value in an attribute, while others have to compute it.

A classic demonstration of this is two classes for representing vectors, either using cartesian or polar coordinates. By accessing the coordinates using methods, you can interchange them.

import math

class cartesian_vector():
    def __init__(self, x, y):
        self.x = x
        self.y = y
    def getX(self):
        return self.x
    def getY(self):
        return self.y
    def getR(self):
        return math.sqrt(self.x**2 + self.y**2)
    def getTheta(self):
        return math.atan(self.y/self.x)

class polar_vector():
    def __init__(self, r, theta):
        self.r = f
        self.theta = theta
    def getX(self):
        return self.r * math.cos(self.theta)
    def getY(self):
        return self.r * math.sin(self.theta)
    def getR(self):
        return self.r
    def getTheta(self):
        return self.theta

Upvotes: 1

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