Overloading equality
When comparing two objects of a custom class using ==, Python by default compares just the memory chunks that the objects point to, not the data contained in the objects. To override this behavior, the class can implement a special method, which accepts two arguments, the objects to be compared, and returns True or False. This method will be implicitly called when two objects are compared.
The BankAccount class from the previous chapter is available for you in the script.py. It has two attributes, balance and number, and a withdraw() method. Two bank accounts with the same balance are not necessarily the same account, but a bank account usually has an account number, and two accounts with the same account number should be considered the same.
This exercise is part of the course
Introduction to Object-Oriented Programming in Python
Exercise instructions
- Modify the
__init__()method to accept a new argument callednumberand initialize a newnumberattribute. - Define a method to compare if the
numberattribute of two objects are equal.
Hands-on interactive exercise
Have a go at this exercise by completing this sample code.
class BankAccount:
# Modify to initialize a number attribute
def __init__(self, ____, balance=0):
self.balance = balance
____
def withdraw(self, amount):
self.balance -= amount
# Define __eq__ that returns True if the number attributes are equal
def ____(____, ____):
return ____.number == ____.____
# Create accounts and compare them
acct1 = BankAccount(123, 1000)
acct2 = BankAccount(123, 1000)
acct3 = BankAccount(456, 1000)
print(acct1 == acct2)
print(acct1 == acct3)