Object-Oriented Programming Ali Taheri Sharif University of - - PowerPoint PPT Presentation

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Object-Oriented Programming Ali Taheri Sharif University of - - PowerPoint PPT Presentation

Sep 19, 2022 223 likes •482 views

Fu Fundamentals of Pr Programming (Py Python) Object-Oriented Programming Ali Taheri Sharif University of Technology Spring 2019 Outline 1. Python Data Types 8. Composition 2. Classes and Objects 9. Mutability 3. Defining Classes

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SLIDE 1

Fu Fundamentals of Pr Programming (Py Python)

Object-Oriented Programming

Ali Taheri Sharif University of Technology

Spring 2019

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Outline

  • 1. Python Data Types
  • 2. Classes and Objects
  • 3. Defining Classes
  • 4. Working with Objects
  • 5. Customizing Initializer
  • 6. Adding Methods
  • 7. Special Methods
  • 8. Composition
  • 9. Mutability

10.Sameness 11.Copying

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ALI TAHERI - FUNDAMENTALS OF PROGRAMMING [PYTHON] Spring 2019

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SLIDE 3

Python Data Types

So far we have seen several data types in Python Some of these data types are primitive data types

  • Integer, Float, String, Boolean

Some of them are more complicated

  • List, Dictionary, Set, File

In Python, we can build our own data types

  • Using the other available types
  • This is the subject of Object-Oriented programming

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Classes and Objects

An object is simply a variable A Class is simply a data type of an object We have been using objects!

  • Just didn’t call them objects

For example: str is a data type (or class)

  • We created objects of type (class) string

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ALI TAHERI - FUNDAMENTALS OF PROGRAMMING [PYTHON] Spring 2019

animal = "cow" fruit = "apple"

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Classes and Objects

Object vs Variable

  • Objects may contain variables, called attributes
  • Objects may contain methods

Class vs Type

  • Programmer can define his own classes
  • Attributes and methods are defined within class

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ALI TAHERI - FUNDAMENTALS OF PROGRAMMING [PYTHON] Spring 2019

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Defining Classes

Class header

  • Keyword class begins definition
  • Followed by name of class and colon ( : )

Initializer method __init__

  • Executes each time an object is created
  • Initializes attributes of class

Object reference

  • All methods must at least specify this one parameter
  • Represents object of class from which a method is called
  • Called self by convention

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ALI TAHERI - FUNDAMENTALS OF PROGRAMMING [PYTHON] Spring 2019

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Defining Classes

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ALI TAHERI - FUNDAMENTALS OF PROGRAMMING [PYTHON] Spring 2019

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Working with Objects

Instantiating objects: Accessing objects’ attributes:

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ALI TAHERI - FUNDAMENTALS OF PROGRAMMING [PYTHON] Spring 2019

p = Point() q = Point() p.x = 3 q.x = p.y + 5 q.y = p.x * q.x print(p.x, p.y, q.x, q.y)

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Customizing Initializer

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SLIDE 10

Adding Methods

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ALI TAHERI - FUNDAMENTALS OF PROGRAMMING [PYTHON] Spring 2019

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Adding Methods

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ALI TAHERI - FUNDAMENTALS OF PROGRAMMING [PYTHON] Spring 2019

class Point: def __init__(self, x=0, y=0): self.x = x self.y = y def distance_from_origin(self): return ((self.x**2) + (self.y**2)) ** 0.5 def distance(self, other): dx = self.x - other.x dy = self.y - other.y return (dx**2 + dx**2) ** 0.5 p = Point(2, 6) q = Point(-1, 4) d = p.distance(q) print(d)

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Special Methods

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ALI TAHERI - FUNDAMENTALS OF PROGRAMMING [PYTHON] Spring 2019

Operator Method Description

+ __add__(self, other) Addition

  • __sub__(self, other)

Subtraction * __mul__(self, other) Multiplication / __truediv__(self, other) Division < __lt__(self, other) Less than <= __le__(self, other) Less that or equal > __gt__(self, other) Greater than >= __ge__(self, other) Greater than or equal == __eq__(self, other) Equal to != __ne__(self, other) Not equal to

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Special Methods

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ALI TAHERI - FUNDAMENTALS OF PROGRAMMING [PYTHON] Spring 2019

Operator Method Description

[index] __getitem__(self, index) Index operator in __contains__(self, value) Check membership len __len__(self) The number of elements str __str__(self) The string representation

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Special Methods

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ALI TAHERI - FUNDAMENTALS OF PROGRAMMING [PYTHON] Spring 2019

class Point: def __init__(self, x=0, y=0): self.x = x self.y = y def __str__(self): return '(%d,%d)' % (self.x, self.y) def __getitem__(self, index): if index == 0: return self.x elif index == 1: return self.y else: raise IndexError('Point index out of range.') >>> p = Point(2,3) >>> print(p) (2,3) >>> print(p[1]) 3

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Composition

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Mutability

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Sameness

When dealing with objects, the concept of sameness can be ambiguous

  • Do the two objects contain the same data?
  • Do they represent the same object?

Shallow Equality

  • Only compares the references, not the contents of the objects

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Sameness

The equality operator (==) performs shallow equality check by default on user-defined classes

  • Unless the __eq__() method is implemented

Deep Equality

  • Compares the contents of the objects
  • Must be implemented manually through __eq__() or another

custom method

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ALI TAHERI - FUNDAMENTALS OF PROGRAMMING [PYTHON] Spring 2019

>>> p = Point(2,3) >>> q = Point(2,3) >>> p == q False

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Sameness

Deep Equality

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ALI TAHERI - FUNDAMENTALS OF PROGRAMMING [PYTHON] Spring 2019

>>> p = Point(2,3) >>> q = Point(2,3) >>> p == q True class Point: def __init__(self, x=0, y=0): self.x = x self.y = y def __eq__(self, other): return (self.x == other.x and self.y == other.y)

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Copying

The assignment operator make aliases

  • Changing one results in changing the other
  • What if we want separate duplicates?

We can copy objects using the copy module

  • Shallow copy
  • Deep copy

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ALI TAHERI - FUNDAMENTALS OF PROGRAMMING [PYTHON] Spring 2019

>>> p = Point(2,3) >>> q = p >>> p is q True

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Copying

The assignment operator make aliases

  • Changing one results in changing the other
  • What if we want separate duplicates?

We can copy objects using the copy module

  • Shallow copy
  • Deep copy

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ALI TAHERI - FUNDAMENTALS OF PROGRAMMING [PYTHON] Spring 2019

>>> p = Point(2,3) >>> q = p >>> q.x = 5 >>> print(p) (5,3)

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Copying

Shallow Copy

  • Copies the object, but doesn’t copy the embedded objects unless

they are immutable

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Copying

Deep Copy

  • Copies the object, and recursively copies the embedded objects

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ALI TAHERI - FUNDAMENTALS OF PROGRAMMING [PYTHON] Spring 2019

class Rectangle: """ A class to manufacture rectangle objects """ def __init__(self, corner, w, h): self.corner = corner self.width = w self.height = h def __eq__(self, other): return (self.corner == other.corner and self.width == other.width and self.height == other.height)

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Copying

Deep Copy

  • Copies the object, and recursively copies the embedded objects

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ALI TAHERI - FUNDAMENTALS OF PROGRAMMING [PYTHON] Spring 2019

>>> import copy >>> r = Rectangle(Point(1,4), 7, 2) >>> s = copy.copy(r) >>> r == s True >>> s.corner.x = 5 >>> r == s True >>> t = copy.deepcopy(r) >>> r == t True >>> t.corner.x = 6 >>> r == t False