Call other methods within the class

Not only we can refer to instance variables inside a class using self.variable, we can also access other methods inside the same class.

Again, self is how we refer to things in the class from within itself (such as self.variable and self.method).

We will use an example to show how to access other methods inside the same class.

Marble_bag class

(remember docstring? Class can have docstring to explain itself) :

# Marble_bag
class Marble_bag:
    """I have some base marbles in my bag.

    I put more and more marbles into my bag."""

    def __init__(self, base):
        self.total = base

    def put(self, m):
        self.total += m
        return self.total

    def putTwice(self, n):
        self.put(n)
        self.put(n)
        return self.total

Here in Marble_bag class, in __init__, we define object variable using self.total and assign a value base to it as the base number of the marbles.

Then we define the second method put(self, m), in put(), we refer to object variable total using self.total.

The same thing, in the third method putTwice(self, n), we may call other method(put(self,m)) inside the same class by using self.put(n). The self indicates that put() is of the same object as putTwice() is called on.

Please note

when we call self.put(n), we only provide value(n) for variable m specified in put(self, m), no need to provide value for parameter self

Let's make a Marble_bag object:

# create a new object 'myBag'
myBag = Marble_bag(5)
print( myBag.total )       # 5 (base number)

myBag.put(10)
print( myBag.total )         # 15 (total: 5 + 10 )

myBag.putTwice(15)
print( myBag.total )          # 45 (total: 5+10+15+15 )

First, we create a Marble_bag instance: named it myBag, and initialize it with value 5, so we have base number: 5 marbles in myBag.

Then we call the method put(10) to put more marbles in myBag. When we call the methods of the object, we don't need to include the self argument, only provide value for other input argument. Now the total is 15.

Last, we call another method putTwice(15), this method in turn calls put(15) of the same object twice using self.put(15) to put 15 and another 15 in this object. So myBag now has total of 45 marbles ( 5+10+15+15)