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README.md

0x06. Python - Classes and Objects

Python OOP

  • By Guillaume

Background Context

OOP is a totally new concept for all of you (especially those who think they know about it :)). It's VERY important that you read at least all the material that is listed bellow (and skip what we recommend you to skip, you will see them later in the curriculum).

As usual, make sure you type (never copy and paste), test, understand all examples shown in the following links (including those in the video), test again etc. The biggest and most important takeaway of this project is: experiment by yourself OOP, play with it!

Read or watch the below resources in the order presented.

Resources

Read or watch:

Learning Objectives

At the end of this project, you are expected to be able to explain to anyone, without the help of Google:

General

  • Why Python programming is awesome
  • What is OOP
  • "first-class everything"
  • What is a class
  • What is an object and an instance
  • What is the difference between a class and an object or instance
  • What is an attribute
  • What are and how to use public, protected and private attributes
  • What is self
  • What is a method
  • What is the special __init__ method and how to use it
  • What is Data Abstraction, Data Encapsulation, and Information Hiding
  • What is a property
  • What is the difference between an attribute and a property in Python
  • What is the Pythonic way to write getters and setters in Python
  • How to dynamically create arbitrary new attributes for existing instances of a class
  • How to bind attributes to object and classes
  • What is the __dict__ of a class and/or instance of a class and what does it contain
  • How does Python find the attributes of an object or class
  • How to use the getattr function

Copyright - Plagiarism

  • You are tasked to come up with solutions for the tasks below yourself to meet with the above learning objectives.
  • You will not be able to meet the objectives of this or any following project by copying and pasting someone else's work.
  • You are not allowed to publish any content of this project.
  • Any form of plagiarism is strictly forbidden and will result in removal from the program.

Requirements

General

  • Allowed editors: vi, vim, emacs
  • All your files will be interpreted/compiled on Ubuntu 20.04 LTS using python3 (version 3.8.5)
  • All your files should end with a new line
  • The first line of all your files should be exactly #!/usr/bin/python3
  • A README.md file, at the root of the folder of the project, is mandatory
  • Your code should use the pycodestyle (version 2.8.*)
  • All your files must be executable
  • The length of your files will be tested using wc
  • All your modules should have a documentation (python3 -c 'print(__import__("my_module").__doc__)')
  • All your classes should have a documentation (python3 -c 'print(__import__("my_module").MyClass.__doc__)')
  • All your functions (inside and outside a class) should have a documentation (python3 -c 'print(__import__("my_module").my_function.__doc__)' and python3 -c 'print(__import__("my_module").MyClass.my_function.__doc__)')
  • A documentation is not a simple word, it's a real sentence explaining what's the purpose of the module, class or method (the length of it will be verified)

More Info

Documentation is now mandatory! Each module, class, and method must contain docstring as comments. Example Google Style Python Docstrings

Tasks

0. My first square

mandatory

Write an empty class Square that defines a square:

  • You are not allowed to import any module
guillaume@ubuntu:~/0x06$ cat 0-main.py
#!/usr/bin/python3
Square = __import__('0-square').Square

my_square = Square()
print(type(my_square))
print(my_square.__dict__)

guillaume@ubuntu:~/0x06$ ./0-main.py
<class '0-square.Square'>
{}
guillaume@ubuntu:~/0x06$

Repo:

  • GitHub repository: alx-higher_level_programming
  • Directory: 0x06-python-classes
  • File: 0-square.py

1. Square with size

mandatory

Write a class Square that defines a square by: (based on 0-square.py)

  • Private instance attribute: size
  • Instantiation with size (no type/value verification)
  • You are not allowed to import any module

Why?

Why size is private attribute?

The size of a square is crucial for a square, many things depend of it (area computation, etc.), so you, as class builder, must control the type and value of this attribute. One way to have the control is to keep it privately. You will see in next tasks how to get, update and validate the size value.

guillaume@ubuntu:~/0x06$ cat 1-main.py
#!/usr/bin/python3
Square = __import__('1-square').Square

my_square = Square(3)
print(type(my_square))
print(my_square.__dict__)

try:
    print(my_square.size)
except Exception as e:
    print(e)

try:
    print(my_square.__size)
except Exception as e:
    print(e)

guillaume@ubuntu:~/0x06$ ./1-main.py
<class '1-square.Square'>
{'_Square__size': 3}
'Square' object has no attribute 'size'
'Square' object has no attribute '__size'
guillaume@ubuntu:~/0x06$

Repo:

  • GitHub repository: alx-higher_level_programming
  • Directory: 0x06-python-classes
  • File: 1-square.py

2. Size validation

mandatory

Write a class Square that defines a square by: (based on 1-square.py)

  • Private instance attribute: size
  • Instantiation with optional size: def __init__(self, size=0):

    • size must be an integer, otherwise raise a TypeError exception with the message size must be an integer

    • if size is less than 0, raise a ValueError exception with the message size must be >= 0

  • You are not allowed to import any module
guillaume@ubuntu:~/0x06$ cat 2-main.py
#!/usr/bin/python3
Square = __import__('2-square').Square

my_square_1 = Square(3)
print(type(my_square_1))
print(my_square_1.__dict__)

my_square_2 = Square()
print(type(my_square_2))
print(my_square_2.__dict__)

try:
    print(my_square_1.size)
except Exception as e:
    print(e)

try:
    print(my_square_1.__size)
except Exception as e:
    print(e)

try:
    my_square_3 = Square("3")
    print(type(my_square_3))
    print(my_square_3.__dict__)
except Exception as e:
    print(e)

try:
    my_square_4 = Square(-89)
    print(type(my_square_4))
    print(my_square_4.__dict__)
except Exception as e:
    print(e)

guillaume@ubuntu:~/0x06$ ./2-main.py
<class '2-square.Square'>
{'_Square__size': 3}
<class '2-square.Square'>
{'_Square__size': 0}
'Square' object has no attribute 'size'
'Square' object has no attribute '__size'
size must be an integer
size must be >= 0
guillaume@ubuntu:~/0x06$

Repo:

  • GitHub repository: alx-higher_level_programming
  • Directory: 0x06-python-classes
  • File: 2-square.py

3. Area of a square

mandatory

Write a class Square that defines a square by: (based on 2-square.py)

  • Private instance attribute: size
  • Instantiation with optional size: def __init__(self, size=0):

    • size must be an integer, otherwise raise a TypeError exception with the message size must be an integer

    • if size is less than 0, raise a ValueError exception with the message size must be >= 0

  • Public instance method: def area(self): that returns the current square area
  • You are not allowed to import any module
guillaume@ubuntu:~/0x06$ cat 3-main.py
#!/usr/bin/python3
Square = __import__('3-square').Square

my_square_1 = Square(3)
print("Area: {}".format(my_square_1.area()))

try:
    print(my_square_1.size)
except Exception as e:
    print(e)

try:
    print(my_square_1.__size)
except Exception as e:
    print(e)

my_square_2 = Square(5)
print("Area: {}".format(my_square_2.area()))

guillaume@ubuntu:~/0x06$ ./3-main.py
Area: 9
'Square' object has no attribute 'size'
'Square' object has no attribute '__size'
Area: 25
guillaume@ubuntu:~/0x06$

Repo:

  • GitHub repository: alx-higher_level_programming
  • Directory: 0x06-python-classes
  • File: 3-square.py

4. Access and update private attribute

mandatory

Write a class Square that defines a square by: (based on 3-square.py)

  • Private instance attribute: size:
    • property def size(self): to retrieve it
    • property setter def size(self, value): to set it:

      • size must be an integer, otherwise raise a TypeError exception with the message size must be an integer

      • if size is less than 0, raise a ValueError exception with the message size must be >= 0

  • Instantiation with optional size: def __init__(self, size=0):
  • Public instance method: def area(self): that returns the current square area
  • You are not allowed to import any module

Why?

Why a getter and setter?

Reminder: size is a private attribute. We did that to make sure we control the type and value. Getter and setter methods are not 100% Python, but more OOP. With them, you will be able to validate the assignment of a private attribute and also define how getting the attribute value will be available from outside - by copy? by assignment? etc. Also, adding type/value validation in the setter will centralize the logic, since you will do it in only one place.

guillaume@ubuntu:~/0x06$ cat 4-main.py
#!/usr/bin/python3
Square = __import__('4-square').Square

my_square = Square(89)
print("Area: {} for size: {}".format(my_square.area(), my_square.size))

my_square.size = 3
print("Area: {} for size: {}".format(my_square.area(), my_square.size))

try:
    my_square.size = "5 feet"
    print("Area: {} for size: {}".format(my_square.area(), my_square.size))
except Exception as e:
    print(e)

guillaume@ubuntu:~/0x06$ ./4-main.py
Area: 7921 for size: 89
Area: 9 for size: 3
size must be an integer
guillaume@ubuntu:~/0x06$

Repo:

  • GitHub repository: alx-higher_level_programming
  • Directory: 0x06-python-classes
  • File: 4-square.py

5. Printing a square

mandatory

Write a class Square that defines a square by: (based on 4-square.py)

  • Private instance attribute: size:
    • property def size(self): to retrieve it
    • property setter def size(self, value): to set it:

      • size must be an integer, otherwise raise a TypeError exception with the message size must be an integer

      • if size is less than 0, raise a ValueError exception with the message size must be >= 0

  • Instantiation with optional size: def __init__(self, size=0):
  • Public instance method: def area(self): that returns the current square area
  • Public instance method: def my_print(self): that prints in stdout the square with the character #:
    • if size is equal to 0, print an empty line
  • You are not allowed to import any module
guillaume@ubuntu:~/0x06$ cat 5-main.py
#!/usr/bin/python3
Square = __import__('5-square').Square

my_square = Square(3)
my_square.my_print()

print("--")

my_square.size = 10
my_square.my_print()

print("--")

my_square.size = 0
my_square.my_print()

print("--")

guillaume@ubuntu:~/0x06$ ./5-main.py
###
###
###
--
##########
##########
##########
##########
##########
##########
##########
##########
##########
##########
--

--
guillaume@ubuntu:~/0x06$

Repo:

  • GitHub repository: alx-higher_level_programming
  • Directory: 0x06-python-classes
  • File: 5-square.py

6. Coordinates of a square

mandatory

Write a class Square that defines a square by: (based on 5-square.py)

  • Private instance attribute: size:

    • property def size(self): to retrieve it
    • property setter def size(self, value): to set it:

      • size must be an integer, otherwise raise a TypeError exception with the message size must be an integer

      • if size is less than 0, raise a ValueError exception with the message size must be >= 0

  • Private instance attribute: position:

    • property def position(self): to retrieve it
    • property setter def position(self, value): to set it:
      • position must be a tuple of 2 positive integers, otherwise raise a TypeError exception with the message position must be a tuple of 2 positive integers

  • Instantiation with optional size and optional position: def __init__(self, size=0, position=(0, 0)):

  • Public instance method: def area(self): that returns the current square area

  • Public instance method: def my_print(self): that prints in stdout the square with the character #:

    • if size is equal to 0, print an empty line
    • position should be use by using space - Don't fill lines by spaces when position[1] > 0

  • You are not allowed to import any module

guillaume@ubuntu:~/0x06$ cat 6-main.py
#!/usr/bin/python3
Square = __import__('6-square').Square

my_square_1 = Square(3)
my_square_1.my_print()

print("--")

my_square_2 = Square(3, (1, 1))
my_square_2.my_print()

print("--")

my_square_3 = Square(3, (3, 0))
my_square_3.my_print()

print("--")

guillaume@ubuntu:~/0x06$ ./6-main.py | tr " " "_" | cat -e
###$
###$
###$
--$
$
_###$
_###$
_###$
--$
___###$
___###$
___###$
--$
guillaume@ubuntu:~/0x06$

Repo:

  • GitHub repository: alx-higher_level_programming
  • Directory: 0x06-python-classes
  • File: 6-square.py