What is OOP?

O B J E C T- O R I E N T E D P R O G R A M M I N G I N P Y T H O N

Alex Yarosh
Content Quality Analyst @ DataCamp
 

Procedural programming
 

Code as a sequence of steps

Great for data analysis

OBJECT-ORIENTED PROGRAMMING IN PYTHON

Thinking in sequences
   

OBJECT-ORIENTED PROGRAMMING IN PYTHON

   

Procedural programming Object-oriented programming

   

Code as a sequence of steps Code as interactions of objects

Great for data analysis and scripts Great for building frameworks and tools

Maintainable and reusable code!

OBJECT-ORIENTED PROGRAMMING IN PYTHON

Objects as data structures
Object = state + behavior

Encapsulation - bundling data with code operating on it

OBJECT-ORIENTED PROGRAMMING IN PYTHON

Classes as blueprints
Class : blueprint for objects outlining possible states and behaviors

OBJECT-ORIENTED PROGRAMMING IN PYTHON

Classes as blueprints
Class : blueprint for objects outlining possible states and behaviors

OBJECT-ORIENTED PROGRAMMING IN PYTHON

Objects in Python
Everything in Python is an object Object Class
Every object has a class
5 int
Use type() to nd the class
"Hello" str
import numpy as np
pd.DataFrame() DataFrame
a = np.array([1,2,3,4])
print(type(a)) np.mean function

... ...
numpy.ndarray

OBJECT-ORIENTED PROGRAMMING IN PYTHON

Attributes and methods
State ↔ attributes Behavior ↔ methods

import numpy as np import numpy as np

a = np.array([1,2,3,4]) a = np.array([1,2,3,4])

# shape attribute # reshape method

a.shape a.reshape(2,2)

(4,) array([[1, 2],

[3, 4]])
 

Use obj. to access attributes and

methods

OBJECT-ORIENTED PROGRAMMING IN PYTHON

Object = attributes + methods
attribute ↔ variables ↔ obj.my_attribute ,

method ↔ function() ↔ obj.my_method() .

import numpy as np
a = np.array([1,2,3,4])
dir(a) # <--- list all attributes and methods

['T',
'__abs__',
...
'trace',
'transpose',
'var',
'view']

OBJECT-ORIENTED PROGRAMMING IN PYTHON

 Let's review!
O B J E C T- O R I E N T E D P R O G R A M M I N G I N P Y T H O N
 Class anatomy:
attributes and
methods
O B J E C T- O R I E N T E D P R O G R A M M I N G I N P Y T H O N

Alex Yarosh
Content Quality Analyst @ DataCamp
A basic class
class <name>: starts a class de nition
class Customer:

# code for class goes here code inside class is indented

pass use pass to create an "empty" class

c1 = Customer()
use ClassName() to create an object of class
c2 = Customer() ClassName

OBJECT-ORIENTED PROGRAMMING IN PYTHON

Add methods to a class
class Customer: method de nition = function de nition within
class
def identify(self, name):
use self as the 1st argument in method
print("I am Customer " + name)
de nition

cust = Customer() ignore self when calling method on an

cust.identify("Laura") object

I am Customer Laura

OBJECT-ORIENTED PROGRAMMING IN PYTHON

class Customer:

def identify(self, name):

print("I am Customer " + name)

cust = Customer()
cust.identify("Laura")

What is self?
classes are templates, how to refer data of a particular object?

self is a stand-in for a particular object used in class de nition

should be the rst argument of any method

Python will take care of self when method called from an object:

cust.identify("Laura") will be interpreted as Customer.identify(cust, "Laura")

OBJECT-ORIENTED PROGRAMMING IN PYTHON

We need attributes
Encapsulation: bundling data with methods that operate on data

E.g. Customer 's' name should be an attribute

 
Attributes are created by assignment (=) in methods

OBJECT-ORIENTED PROGRAMMING IN PYTHON

Add an attribute to class
class Customer:
# set the name attribute of an object to new_name
def set_name(self, new_name):

# Create an attribute by assigning a value

self.name = new_name # <-- will create .name when set_name is called

cust = Customer() # <--.name doesn't exist here yet

cust.set_name("Lara de Silva") # <--.name is created and set to "Lara de Silva"

print(cust.name) # <--.name can be used

Lara de Silva

OBJECT-ORIENTED PROGRAMMING IN PYTHON

Old version New version
class Customer: class Customer:
def set_name(self, new_name):
self.name = new_name

# Using a parameter # Using .name from the object it*self*

def identify(self, name): def identify(self):
print("I am Customer" + name) print("I am Customer" + self.name)

cust = Customer() cust = Customer()

cust.set_name("Rashid Volkov")
cust.identify("Eris Odoro") cust.identify()

I am Customer Eris Odoro I am Customer Rashid Volkov

OBJECT-ORIENTED PROGRAMMING IN PYTHON

 Let's practice!
O B J E C T- O R I E N T E D P R O G R A M M I N G I N P Y T H O N
 Class anatomy: the
__init__ constructor
O B J E C T- O R I E N T E D P R O G R A M M I N G I N P Y T H O N

Alex Yarosh
Content Quality Analyst @ DataCamp
Methods and attributes
Methods are function de nitions within a class class MyClass:
# function definition in class
self as the rst argument
# first argument is self
De ne attributes by assignment def my_method1(self, other_args...):
# do things here
Refer to attributes in class via self.___

   def my_method2(self, my_attr):

# attribute created by assignment
self.my_attr = my_attr
...

OBJECT-ORIENTED PROGRAMMING IN PYTHON

Constructor
Add data to object when creating it?

Constructor __init__() method is called every time an object is created.

class Customer:
def __init__(self, name):
self.name = name # <--- Create the .name attribute and set it to name parameter
print("The __init__ method was called")

cust = Customer("Lara de Silva") #<--- __init__ is implicitly called

print(cust.name)

The __init__ method was called

Lara de Silva

OBJECT-ORIENTED PROGRAMMING IN PYTHON

class Customer:
def __init__(self, name, balance): # <-- balance parameter added

self.name = name
self.balance = balance # <-- balance attribute added
print("The __init__ method was called")

cust = Customer("Lara de Silva", 1000) # <-- __init__ is called

print(cust.name)
print(cust.balance)

The __init__ method was called

Lara de Silva
1000

OBJECT-ORIENTED PROGRAMMING IN PYTHON

class Customer:
def __init__(self, name, balance=0): #<--set default value for balance

self.name = name
self.balance = balance
print("The __init__ method was called")

cust = Customer("Lara de Silva") # <-- don't specify balance explicitly

print(cust.name)
print(cust.balance) # <-- attribute is created anyway

The __init__ method was called

Lara de Silva
0

OBJECT-ORIENTED PROGRAMMING IN PYTHON

Attributes in methods Attributes in the constructor
class MyClass: class MyClass:
def my_method1(self, attr1): def __init__(self, attr1, attr2):
self.attr1 = attr1 self.attr1 = attr1
... self.attr2 = attr2
...
def my_method2(self, attr2): # All attributes are created
self.attr2 = attr2 obj = MyClass(val1, val2)
...

easier to know all the attributes

obj = MyClass() attributes are created when the object is
obj.my_method1(val1) # <-- attr1 created
created
obj.my_method2(val2) # <-- attr2 created
more usable and maintainable code

OBJECT-ORIENTED PROGRAMMING IN PYTHON

Best practices
1. Initialize attributes in __init__()

OBJECT-ORIENTED PROGRAMMING IN PYTHON

Best practices
1. Initialize attributes in __init__()

2. Naming
CamelCase for classes, lower_snake_case for functions and attributes

OBJECT-ORIENTED PROGRAMMING IN PYTHON

Best practices
1. Initialize attributes in __init__()

2. Naming
CamelCase for class, lower_snake_case for functions and attributes

3. Keep self as self

class MyClass:
# This works but isn't recommended
def my_method(kitty, attr):
kitty.attr = attr

OBJECT-ORIENTED PROGRAMMING IN PYTHON

Best practices
1. Initialize attributes in __init__()

2. Naming
CamelCase for class, lower_snake_case for functions and attributes

3. self is self

4. Use docstrings
class MyClass:
"""This class does nothing"""
pass

OBJECT-ORIENTED PROGRAMMING IN PYTHON

 Let's practice!
O B J E C T- O R I E N T E D P R O G R A M M I N G I N P Y T H O N