Overloading equality
When comparing two objects of a custom class using ==, Python by default compares just the object references, not the data contained in the objects. To override this behavior, the class can implement the special __eq__() 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 pane. It has one attribute, balance, 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 is a part of the course
“Object-Oriented Programming in Python”
Exercise instructions
Try selecting the code in lines 1-7 and pressing the "Run code" button. Then try to create a few BankAccount objects in the console and compare them.
- Modify the
__init__()method to accept a new parameter -number- and initialize a newnumberattribute. - Define an
__eq__()method that returnsTrueif thenumberattribute of two objects is equal. - Examine the print statements and the output in the console.
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)
This exercise is part of the course
Object-Oriented Programming in Python
Dive in and learn how to create classes and leverage inheritance and polymorphism to reuse and optimize code.
In this chapter, you'll learn how to make sure that objects that store the same data are considered equal, how to define and customize string representations of objects, and even how to create new error types. Through interactive exercises, you’ll learn how to further customize your classes to make them work more like standard Python data types.
Exercise 1: Operator overloading: comparisonExercise 2: Overloading equalityExercise 3: Checking class equalityExercise 4: Comparison and inheritanceExercise 5: Operator overloading: string representationExercise 6: String formatting reviewExercise 7: String representation of objectsExercise 8: ExceptionsExercise 9: Catching exceptionsExercise 10: Custom exceptionsExercise 11: Handling exception hierarchiesWhat is DataCamp?
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