Python language basics 75: class level methods

Introduction

In the previous post we looked at the basics of validation. In particular we looked at an example where the values sent to the initialiser were validated in code. Validation is important in order to stop invalid values being assigned to class level variables. However, validation can occur just about anywhere in code. E.g. if a numeric input is required from the user then you’d almost certainly need to validate it so that the code doesn’t stop with an exception when trying to convert the string input into a number.

In this post we’ll quickly look at class level methods.

Class level methods

Class level methods are in fact not much different from other methods we’ve seen so far. Here’s an example of a method that returns an integer:

def add_two_numbers(firstNumber, secondNumber):
    return firstNumber + secondNumber

We’ve already seen a class level method in our Person class:

def shout(self):
        print("HELLOOOOO")

The “self” argument will turn the method into a class method that operates on the object itself that was created from the class. It always comes first but is not supplied to the method in code:

person = Person("John", 100)
person.shout()

All “real” parameters that the method requires must be added after “self”:

def shout(self, what, how_many_times):
        for i in range(0,how_many_times):
            print(what)

Here’s an example of calling the method:

person = Person("John", 100)
person.shout("Hello", 4)

…which gives the following output:

Hello
Hello
Hello
Hello

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