General Methods

General Methods#

A method is a function, which is defined for a class and can only be called on an instance.

Defining a Method#

Methods are defined like regular functions but must be within the class definition block and their first parameter must be self.

class ClassName:

    def method1(self, parameter_1, ..., parameter_n):
        # do something
        return # optional

    def method2(self, parameter_1, ..., parameter_n):
        # do something
        return # optional

Note

You’ve already defined a method before. __init__ is a special method that is called when the object is created!

Self#

The self parameter of __init__ is a variable that references the current instance that is being created. Recall that a class definition is a blueprint, so self is a way of specifying which instance is being affected by the blueprint.

Calling a Method#

Methods are called by using using . between the instance object and the method name.

instance.method(argument_1, ..., argument_n)

Example: Depositing funds

In the example below, the deposit method has been added the Account class. This method takes one parameter amount, which is used to increase the balance attribute.

class Account:

    def __init__(self, bsb_number, account_number, balance, holder_name):
        self.bsb_number = bsb_number
        self.account_number = account_number
        self.balance = balance
        self.holder_name = holder_name

    def deposit(self, amount):
        self.balance += amount


batman_account = Account("689716", "62228626", 19.39, "Bruce Wayne")
batman_account.deposit(10)  # Calling deposit with amount=10
print(batman_account.balance)

../../_images/full_bank_account_deposit.png

Many Methods#

We can add as many methods as we like to our classes.

Example

In the example below, a withdraw method has been added to work in tandem with deposit.

class Account:

    def __init__(self, bsb_number, account_number, balance, holder_name):
        self.bsb_number = bsb_number
        self.account_number = account_number
        self.balance = balance
        self.holder_name = holder_name

    def deposit(self, amount):
        self.balance += amount

    def withdraw(self, amount):
        self.balance -= amount
        if self.balance < 0:
            print("WARNING: Account is overdrawn!")


batman_account = Account("689716", "62228626", 19.39, "Bruce Wayne")
batman_account.deposit(10)
batman_account.withdraw(5.39)
print(batman_account.balance)

../../_images/full_bank_account_deposit_withdraw.png

Fruitful Methods#

Just like other functions, methods can return a value - we call these “fruitful” functions.

Example

The example below includes get_earned_interest, which returns the interest amount on the current balance the account holder is owed. This value is returned outside the instance and does not affect any instance attributes.

class Account:

    def __init__(self, bsb_number, account_number, balance, holder_name):
        self.bsb_number = bsb_number
        self.account_number = account_number
        self.balance = balance
        self.holder_name = holder_name

    def get_earned_interest(self):
        interest_rate = 0.0235
        return interest_rate * self.balance


batman_account = Account("689716", "62228626", 19.39, "Bruce Wayne")
interest = batman_account.get_earned_interest()
print(interest)