Operator overloading: string representation

Object-Oriented Programming in Python

Alex Yarosh

Content Quality Analyst @ DataCamp

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>

import numpy as np

arr = np.array([1,2,3])
print(arr)

[1 2 3]

`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()

Implementation: str

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

  def __str__(self):
    cust_str = """
    Customer:
      name: {name}
      balance: {balance}
    """.format(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

Implementation: repr

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

  def __repr__(self):
    # Notice the '...' around name 
    return "Customer('{name}', {balance})".format(name = self.name, balance = self.balance)

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

Customer('Maryam Azar', 3000) # <--- not Customer(Maryam Azar, 3000)

Surround string arguments with quotation marks in the __repr__() output

Let's practice!

Object-Oriented Programming in Python