Inheritance comparison and string representation

Introduzione alla programmazione orientata agli oggetti in Python

George Boorman

Curriculum Manager, DataCamp

Comparing objects from different classes

class Customer:
    def __init__(self, acc_id, name):
        self.acc_id, self.name = acc_id, name

    def __eq__(self, other):
        # Returns True if the objects have the same attributes
        # and are of the same type
        return (self.acc_id == other.acc_id) and (self.name == other.name)\
            and (type(self) == type(other))
Introduzione alla programmazione orientata agli oggetti in Python

Comparing objects with inheritance

 

 

 

                               

    What if one object inherits from the class of the other object?

Introduzione alla programmazione orientata agli oggetti in Python

Bank and savings accounts

SavingsAccount inheriting from BankAccount

Introduzione alla programmazione orientata agli oggetti in Python

__eq__ in parent/child classes

class BankAccount:
    def __init__(self, number, balance=0):
        self.balance = balance
        self.number = number

    def withdraw(self, amount):
        self.balance -= amount 

    # Define __eq__ that returns True 
    # if the number attributes are equal 
    def __eq__(self, other):
        print("BankAccount __eq__() called")
        return self.number == other.number 

class SavingsAccount(BankAccount):
    def __init__(self, number, balance, interest_rate):
        BankAccount.__init__(self, number,
                             balance)
          self.interest_rate = interest_rate

    # Define __eq__ that returns True 
    # if the number attributes are equal 
    def __eq__(self, other):
        print("SavingsAccount __eq__() called")
        return self.number == other.number
Introduzione alla programmazione orientata agli oggetti in Python

Comparing parent and child objects

ba = BankAccount(123, 10000)
sa = SavingsAccount(456, 2000, 0.05)
# Compare the two objects
ba == sa

SavingsAccount __eq__() called
False

sa == ba

SavingsAccount __eq__() called
False
Introduzione alla programmazione orientata agli oggetti in Python

Printing an object

class Customer:
    def __init__(self, name, balance):
        self.name, self.balance = name, balance 

cust = Customer("Maryam Azar", 3000)
print(cust)

<__main__.Customer at 0x1f8598e2240>





a_list = [1,2,3]
print(a_list)

[1, 2, 3]
Introduzione alla programmazione orientata agli oggetti in Python

__str__()

  • print(obj), str(obj)
print(np.array([1,2,3]))

[1 2 3]

str(np.array([1,2,3]))

'[1 2 3]'
  • informal, for end user
  • string representation

__repr__()

  • repr(obj), printing in console
repr(np.array([1,2,3]))

'array([1,2,3])'

np.array([1,2,3])

array([1, 2, 3])
  • formal, for developer
  • reproducible representation
  • fallback for print()
Introduzione alla programmazione orientata agli oggetti in Python

Implementation: repr

class Customer:
    def __init__(self, name, balance):
        self.name = name
        self.balance = balance 

    def __repr__(self):

        # Notice the '...' around name
        return f"Customer('{self.name}', {self.balance})"


cust = Customer("Maryam Azar", 3000)
# Will implicitly call __repr__()
cust

Customer('Maryam Azar', 3000)
Introduzione alla programmazione orientata agli oggetti in Python

Implementation: str

class Customer:
    def __init__(self, name, balance):
        self.name = name
        self.balance = balance
    def __str__(self):
        cust_str = f"""
        Customer:
            name: {self.name}
            balance: {self.balance}
            """
        return cust_str

cust = Customer("Maryam Azar", 3000)

# Will implicitly call __str__()
print(cust)

Customer:
  name: Maryam Azar
  balance: 3000
Introduzione alla programmazione orientata agli oggetti in Python

Let's practice!

Introduzione alla programmazione orientata agli oggetti in Python

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