Defining and Calling a Function within a Python Class

Question

I'm creating a class and I'm hoping to call a user-defined function within a method for that class. I'd also like to define the function within the class definition. However, when I call the class, I get the error message name *whatever function* is not defined.

For instance, something like this:

class ExampleClass():

    def __init__(self, number):
        self.number = number

    def plus_2_times_4(x):
        return(4*(x + 2))

    def arithmetic(self):
        return(plus_2_times_4(self.number))

But when I call:

instance = ExampleClass(number = 4)
instance.arithmetic() 

I get the error message.

So basically I want to define the function in one step (def plus_2_times_4) and use the function when defining a method in another step (def arithmetic...). Is this possible?

Thanks so much in advance!

Answer 1

Define and call plus_2_times_4 with self, namely:

class ExampleClass():

    def __init__(self, number):
        self.number = number

    def plus_2_times_4(self,x):
        return(4*(x + 2))

    def arithmetic(self):
        return(self.plus_2_times_4(self.number))

This will work.

Answer 2

Call the method using ExampleClass.plus_2_times_4:

class ExampleClass():

    def __init__(self, number):
        self.number = number

    def plus_2_times_4(x):
        return(4*(x + 2))

    def arithmetic(self):
        return(ExampleClass.plus_2_times_4(self.number))

Alternatively, use the @staticmethod decorator and call the method using the normal method calling syntax:

class ExampleClass():

    def __init__(self, number):
        self.number = number

    @staticmethod
    def plus_2_times_4(x):
        return(4*(x + 2))

    def arithmetic(self):
        return(self.plus_2_times_4(self.number))

The @staticmethod decorator ensures that self will never be implicitly passed in, like it normally is for methods.