0x08-python-more_classes

0x08. Python - More Classes and Objects

Python OOP

Resources

Read or watch:

• Object Oriented Programming (Read everything until the paragraph “Inheritance” (excluded))
• Object-Oriented Programming(Please be careful: in most of the following paragraphs, the author shows the way you should not use or write a class, in order to help you better understand some concepts and how everything works in Python 3. Make sure you read only the following paragraphs: “General Introduction,” “First-class Everything,” “A Minimal Class in Python,” “Attributes,” “Methods,” “The __init__ Method,” “Data Abstraction, Data Encapsulation, and Information Hiding,” “__str__- and __repr__-Methods,” “Public- Protected- and Private Attributes,” & “Destructor”)
• Class and Instance Attributes
• classmethods and staticmethods
• Properties vs. Getters and Setters (Mainly the last part “Public instead of Private Attributes”)
• str vs repr

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

0. Simple rectangle

Write an empty class Rectangle that defines a rectangle:

• You are not allowed to import any module

guillaume@ubuntu:~/0x08$ cat 0-main.py
#!/usr/bin/python3
Rectangle = __import__('0-rectangle').Rectangle

my_rectangle = Rectangle()
print(type(my_rectangle))
print(my_rectangle.__dict__)

guillaume@ubuntu:~/0x08$ ./0-main.py
<class '0-rectangle.Rectangle'>
{}
guillaume@ubuntu:~/0x08$

No test cases needed

1. Real definition of a rectangle

Write a class Rectangle that defines a rectangle by: (based on 0-rectangle.py)

• Private instance attribute: width
  • property def width(self): to retrieve it
  • property setter def width(self, value): to set it:
    • width must be an integer, otherwise raise a TypeError exception with the message width must be an integer
    • if width is less than 0, raise a ValueError exception with the message width must be >= 0
• Private instance attribute: height
  • property def height(self): to retrieve it
  • property setter def height(self, value): to set it:
    • height must be an integer, otherwise raise a TypeError exception with the message height must be an integer
    • if height is less than 0, raise a ValueError exception with the message height must be >= 0
• Instantiation with optional width and height: def __init__(self, width=0, height=0):
• You are not allowed to import any module

guillaume@ubuntu:~/0x08$ cat 1-main.py
#!/usr/bin/python3
Rectangle = __import__('1-rectangle').Rectangle

my_rectangle = Rectangle(2, 4)
print(my_rectangle.__dict__)

my_rectangle.width = 10
my_rectangle.height = 3
print(my_rectangle.__dict__)

guillaume@ubuntu:~/0x08$ ./1-main.py
{'_Rectangle__height': 4, '_Rectangle__width': 2}
{'_Rectangle__height': 3, '_Rectangle__width': 10}
guillaume@ubuntu:~/0x08$

No test cases needed

2. Area and Perimeter

Write a class Rectangle that defines a rectangle by: (based on 0-rectangle.py)

• Private instance attribute: width
  • property def width(self): to retrieve it
  • property setter def width(self, value): to set it:
    • width must be an integer, otherwise raise a TypeError exception with the message width must be an integer
    • if width is less than 0, raise a ValueError exception with the message width must be >= 0
• Private instance attribute: height
  • property def height(self): to retrieve it
  • property setter def height(self, value): to set it:
    • height must be an integer, otherwise raise a TypeError exception with the message height must be an integer
    • if height is less than 0, raise a ValueError exception with the message height must be >= 0
• Instantiation with optional width and height: def __init__(self, width=0, height=0):
• Public instance method: def area(self): that returns the rectangle area
• Public instance method: def perimeter(self): that returns the rectangle perimeter:
  • if width or height is equal to 0, perimeter is equal to 0
• You are not allowed to import any module

guillaume@ubuntu:~/0x08$ cat 2-main.py
#!/usr/bin/python3
Rectangle = __import__('2-rectangle').Rectangle

my_rectangle = Rectangle(2, 4)
print("Area: {} - Perimeter: {}".format(my_rectangle.area(), my_rectangle.perimeter()))

print("--")

my_rectangle.width = 10
my_rectangle.height = 3
print("Area: {} - Perimeter: {}".format(my_rectangle.area(), my_rectangle.perimeter()))

guillaume@ubuntu:~/0x08$ ./2-main.py
Area: 8 - Perimeter: 12
--
Area: 30 - Perimeter: 26
guillaume@ubuntu:~/0x08$

No test cases needed

3. String representation

Write a class Rectangle that defines a rectangle by: (based on 0-rectangle.py)

• Private instance attribute: width
  • property def width(self): to retrieve it
  • property setter def width(self, value): to set it:
    • width must be an integer, otherwise raise a TypeError exception with the message width must be an integer
    • if width is less than 0, raise a ValueError exception with the message width must be >= 0
• Private instance attribute: height
  • property def height(self): to retrieve it
  • property setter def height(self, value): to set it:
    • height must be an integer, otherwise raise a TypeError exception with the message height must be an integer
    • if height is less than 0, raise a ValueError exception with the message height must be >= 0
• Instantiation with optional width and height: def __init__(self, width=0, height=0):
• Public instance method: def area(self): that returns the rectangle area
• Public instance method: def perimeter(self): that returns the rectangle perimeter:
  • if width or height is equal to 0, perimeter is equal to 0
• print() and str() should print the rectangle with the character #: (see example below)
  • if width or height is equal to 0, return an empty string
• You are not allowed to import any module

guillaume@ubuntu:~/0x08$ cat 3-main.py
#!/usr/bin/python3
Rectangle = __import__('3-rectangle').Rectangle

my_rectangle = Rectangle(2, 4)
print("Area: {} - Perimeter: {}".format(my_rectangle.area(), my_rectangle.perimeter()))

print(str(my_rectangle))
print(repr(my_rectangle))

print("--")

my_rectangle.width = 10
my_rectangle.height = 3
print(my_rectangle)
print(repr(my_rectangle))

guillaume@ubuntu:~/0x08$ ./3-main.py
Area: 8 - Perimeter: 12
##
##
##
##
<3-rectangle.Rectangle object at 0x7f92a75a2eb8>
--
##########
##########
##########
<3-rectangle.Rectangle object at 0x7f92a75a2eb8>
guillaume@ubuntu:~/0x08$

Object address can be different No test cases needed

4. Eval is magic

Write a class Rectangle that defines a rectangle by: (based on 0-rectangle.py)

• Private instance attribute: width
  • property def width(self): to retrieve it
  • property setter def width(self, value): to set it:
    • width must be an integer, otherwise raise a TypeError exception with the message width must be an integer
    • if width is less than 0, raise a ValueError exception with the message width must be >= 0
• Private instance attribute: height
  • property def height(self): to retrieve it
  • property setter def height(self, value): to set it:
    • height must be an integer, otherwise raise a TypeError exception with the message height must be an integer
    • if height is less than 0, raise a ValueError exception with the message height must be >= 0
• Instantiation with optional width and height: def __init__(self, width=0, height=0):
• Public instance method: def area(self): that returns the rectangle area
• Public instance method: def perimeter(self): that returns the rectangle perimeter:
  • if width or height is equal to 0, perimeter is equal to 0
• print() and str() should print the rectangle with the character #: (see example below)
  • if width or height is equal to 0, return an empty string
• repr() should return a string representation of the rectangle to be able to recreate a new instance by using eval() (see example below)
• You are not allowed to import any module

guillaume@ubuntu:~/0x08$ cat 4-main.py
#!/usr/bin/python3
Rectangle = __import__('4-rectangle').Rectangle

my_rectangle = Rectangle(2, 4)
print(str(my_rectangle))
print("--")
print(my_rectangle)
print("--")
print(repr(my_rectangle))
print("--")
print(hex(id(my_rectangle)))
print("--")

# create new instance based on representation
new_rectangle = eval(repr(my_rectangle))
print(str(new_rectangle))
print("--")
print(new_rectangle)
print("--")
print(repr(new_rectangle))
print("--")
print(hex(id(new_rectangle)))
print("--")

print(new_rectangle is my_rectangle)
print(type(new_rectangle) is type(my_rectangle))

guillaume@ubuntu:~/0x08$ ./4-main.py
##
##
##
##
--
##
##
##
##
--
Rectangle(2, 4)
--
0x7f09ebf7cc88
--
##
##
##
##
--
##
##
##
##
--
Rectangle(2, 4)
--
0x7f09ebf7ccc0
--
False
True
guillaume@ubuntu:~/0x08$

No test cases needed

5. Detect instance deletion

Write a class Rectangle that defines a rectangle by: (based on 0-rectangle.py)

• Private instance attribute: width
  • property def width(self): to retrieve it
  • property setter def width(self, value): to set it:
    • width must be an integer, otherwise raise a TypeError exception with the message width must be an integer
    • if width is less than 0, raise a ValueError exception with the message width must be >= 0
• Private instance attribute: height
  • property def height(self): to retrieve it
  • property setter def height(self, value): to set it:
    • height must be an integer, otherwise raise a TypeError exception with the message height must be an integer
    • if height is less than 0, raise a ValueError exception with the message height must be >= 0
• Instantiation with optional width and height: def __init__(self, width=0, height=0):
• Public instance method: def area(self): that returns the rectangle area
• Public instance method: def perimeter(self): that returns the rectangle perimeter:
  • if width or height is equal to 0, perimeter is equal to 0
• print() and str() should print the rectangle with the character #: (see example below)
  • if width or height is equal to 0, return an empty string
• repr() should return a string representation of the rectangle to be able to recreate a new instance by using eval() (see example below)
• Print the message Bye rectangle... (... being 3 dots not ellipsis) when an instance of Rectangle is deleted
• You are not allowed to import any module

guillaume@ubuntu:~/0x08$ cat 5-main.py
#!/usr/bin/python3
Rectangle = __import__('5-rectangle').Rectangle

my_rectangle = Rectangle(2, 4)
print("Area: {} - Perimeter: {}".format(my_rectangle.area(), my_rectangle.perimeter()))

del my_rectangle

try:
    print(my_rectangle)
except Exception as e:
    print("[{}] {}".format(e.__class__.__name__, e))

guillaume@ubuntu:~/0x08$ ./5-main.py
Area: 8 - Perimeter: 12
Bye rectangle...
[NameError] name 'my_rectangle' is not defined
guillaume@ubuntu:~/0x08$

No test cases needed

6. How many instances

Write a class Rectangle that defines a rectangle by: (based on 0-rectangle.py)

• Private instance attribute: width
  • property def width(self): to retrieve it
  • property setter def width(self, value): to set it:
    • width must be an integer, otherwise raise a TypeError exception with the message width must be an integer
    • if width is less than 0, raise a ValueError exception with the message width must be >= 0
• Private instance attribute: height
  • property def height(self): to retrieve it
  • property setter def height(self, value): to set it:
    • height must be an integer, otherwise raise a TypeError exception with the message height must be an integer
    • if height is less than 0, raise a ValueError exception with the message height must be >= 0
• Public class attribute number_of_instances:
  • Initialized to 0
  • Incremented during each new instance instantiation
  • Decremented during each instance deletion
• Instantiation with optional width and height: def __init__(self, width=0, height=0):
• Public instance method: def area(self): that returns the rectangle area
• Public instance method: def perimeter(self): that returns the rectangle perimeter:
  • if width or height is equal to 0, perimeter is equal to 0
• print() and str() should print the rectangle with the character #: (see example below)
  • if width or height is equal to 0, return an empty string
• repr() should return a string representation of the rectangle to be able to recreate a new instance by using eval() (see example below)
• Print the message Bye rectangle... (... being 3 dots not ellipsis) when an instance of Rectangle is deleted
• You are not allowed to import any module

guillaume@ubuntu:~/0x08$ cat 6-main.py
#!/usr/bin/python3
Rectangle = __import__('6-rectangle').Rectangle

my_rectangle_1 = Rectangle(2, 4)
my_rectangle_2 = Rectangle(2, 4)
print("{:d} instances of Rectangle".format(Rectangle.number_of_instances))
del my_rectangle_1
print("{:d} instances of Rectangle".format(Rectangle.number_of_instances))
del my_rectangle_2
print("{:d} instances of Rectangle".format(Rectangle.number_of_instances))

guillaume@ubuntu:~/0x08$ ./6-main.py
2 instances of Rectangle
Bye rectangle...
1 instances of Rectangle
Bye rectangle...
0 instances of Rectangle
guillaume@ubuntu:~/0x08$

No test cases needed

7. Change representation

Write a class Rectangle that defines a rectangle by: (based on 0-rectangle.py)

• Private instance attribute: width
  • property def width(self): to retrieve it
  • property setter def width(self, value): to set it:
    • width must be an integer, otherwise raise a TypeError exception with the message width must be an integer
    • if width is less than 0, raise a ValueError exception with the message width must be >= 0
• Private instance attribute: height
  • property def height(self): to retrieve it
  • property setter def height(self, value): to set it:
    • height must be an integer, otherwise raise a TypeError exception with the message height must be an integer
    • if height is less than 0, raise a ValueError exception with the message height must be >= 0
• Public class attribute number_of_instances:
  • Initialized to 0
  • Incremented during each new instance instantiation
  • Decremented during each instance deletion
• Public class attribute print_symbol:
  • Initialized to #
  • Used as symbol for string representation
  • Can be any type
• Instantiation with optional width and height: def __init__(self, width=0, height=0):
• Public instance method: def area(self): that returns the rectangle area
• Public instance method: def perimeter(self): that returns the rectangle perimeter:
  • if width or height is equal to 0, perimeter is equal to 0
• print() and str() should print the rectangle with the character #: (see example below)
  • if width or height is equal to 0, return an empty string
• repr() should return a string representation of the rectangle to be able to recreate a new instance by using eval() (see example below)
• Print the message Bye rectangle... (... being 3 dots not ellipsis) when an instance of Rectangle is deleted
• You are not allowed to import any module

guillaume@ubuntu:~/0x08$ cat 7-main.py
#!/usr/bin/python3
Rectangle = __import__('7-rectangle').Rectangle

my_rectangle_1 = Rectangle(8, 4)
print(my_rectangle_1)
print("--")
my_rectangle_1.print_symbol = "&"
print(my_rectangle_1)
print("--")

my_rectangle_2 = Rectangle(2, 1)
print(my_rectangle_2)
print("--")
Rectangle.print_symbol = "C"
print(my_rectangle_2)
print("--")

my_rectangle_3 = Rectangle(7, 3)
print(my_rectangle_3)

print("--")

my_rectangle_3.print_symbol = ["C", "is", "fun!"]
print(my_rectangle_3)

print("--")

guillaume@ubuntu:~/0x08$ ./7-main.py
########
########
########
########
--
&&&&&&&&
&&&&&&&&
&&&&&&&&
&&&&&&&&
--
##
--
CC
--
CCCCCCC
CCCCCCC
CCCCCCC
--
['C', 'is', 'fun!']['C', 'is', 'fun!']['C', 'is', 'fun!']['C', 'is', 'fun!']['C', 'is', 'fun!']['C', 'is', 'fun!']['C', 'is', 'fun!']
['C', 'is', 'fun!']['C', 'is', 'fun!']['C', 'is', 'fun!']['C', 'is', 'fun!']['C', 'is', 'fun!']['C', 'is', 'fun!']['C', 'is', 'fun!']
['C', 'is', 'fun!']['C', 'is', 'fun!']['C', 'is', 'fun!']['C', 'is', 'fun!']['C', 'is', 'fun!']['C', 'is', 'fun!']['C', 'is', 'fun!']
--
Bye rectangle...
Bye rectangle...
Bye rectangle...
guillaume@ubuntu:~/0x08$

No test cases needed

8. Compare rectangles

Write a class Rectangle that defines a rectangle by: (based on 0-rectangle.py)

• Private instance attribute: width
  • property def width(self): to retrieve it
  • property setter def width(self, value): to set it:
    • width must be an integer, otherwise raise a TypeError exception with the message width must be an integer
    • if width is less than 0, raise a ValueError exception with the message width must be >= 0
• Private instance attribute: height
  • property def height(self): to retrieve it
  • property setter def height(self, value): to set it:
    • height must be an integer, otherwise raise a TypeError exception with the message height must be an integer
    • if height is less than 0, raise a ValueError exception with the message height must be >= 0
• Public class attribute number_of_instances:
  • Initialized to 0
  • Incremented during each new instance instantiation
  • Decremented during each instance deletion
• Public class attribute print_symbol:
  • Initialized to #
  • Used as symbol for string representation
  • Can be any type
• Instantiation with optional width and height: def __init__(self, width=0, height=0):
• Public instance method: def area(self): that returns the rectangle area
• Public instance method: def perimeter(self): that returns the rectangle perimeter:
  • if width or height is equal to 0, perimeter is equal to 0
• print() and str() should print the rectangle with the character #: (see example below)
  • if width or height is equal to 0, return an empty string
• repr() should return a string representation of the rectangle to be able to recreate a new instance by using eval() (see example below)
• Print the message Bye rectangle... (... being 3 dots not ellipsis) when an instance of Rectangle is deleted
• Static method def bigger_or_equal(rect_1, rect_2): that returns the biggest rectangle based on the area
  • rect_1 must be an instance of Rectangle, otherwise raise a TypeError exception with the message rect_1 must be an instance of Rectangle
  • rect_2 must be an instance of Rectangle, otherwise raise a TypeError exception with the message rect_2 must be an instance of Rectangle
  • Returns rect_1 if both have the same area value
• You are not allowed to import any module

guillaume@ubuntu:~/0x08$ cat 8-main.py
#!/usr/bin/python3
Rectangle = __import__('8-rectangle').Rectangle

my_rectangle_1 = Rectangle(8, 4)
my_rectangle_2 = Rectangle(2, 3)

if my_rectangle_1 is Rectangle.bigger_or_equal(my_rectangle_1, my_rectangle_2):
    print("my_rectangle_1 is bigger or equal to my_rectangle_2")
else:
    print("my_rectangle_2 is bigger than my_rectangle_1")


my_rectangle_2.width = 10
my_rectangle_2.height = 5
if my_rectangle_1 is Rectangle.bigger_or_equal(my_rectangle_1, my_rectangle_2):
    print("my_rectangle_1 is bigger or equal to my_rectangle_2")
else:
    print("my_rectangle_2 is bigger than my_rectangle_1")

guillaume@ubuntu:~/0x08$ ./8-main.py
my_rectangle_1 is bigger or equal to my_rectangle_2
my_rectangle_2 is bigger than my_rectangle_1
Bye rectangle...
Bye rectangle...
guillaume@ubuntu:~/0x08$

No test cases needed

9. A square is a rectangle

Write a class Rectangle that defines a rectangle by: (based on 0-rectangle.py)

• Private instance attribute: width
  • property def width(self): to retrieve it
  • property setter def width(self, value): to set it:
    • width must be an integer, otherwise raise a TypeError exception with the message width must be an integer
    • if width is less than 0, raise a ValueError exception with the message width must be >= 0
• Private instance attribute: height
  • property def height(self): to retrieve it
  • property setter def height(self, value): to set it:
    • height must be an integer, otherwise raise a TypeError exception with the message height must be an integer
    • if height is less than 0, raise a ValueError exception with the message height must be >= 0
• Public class attribute number_of_instances:
  • Initialized to 0
  • Incremented during each new instance instantiation
  • Decremented during each instance deletion
• Public class attribute print_symbol:
  • Initialized to #
  • Used as symbol for string representation
  • Can be any type
• Instantiation with optional width and height: def __init__(self, width=0, height=0):
• Public instance method: def area(self): that returns the rectangle area
• Public instance method: def perimeter(self): that returns the rectangle perimeter:
  • if width or height is equal to 0, perimeter is equal to 0
• print() and str() should print the rectangle with the character #: (see example below)
  • if width or height is equal to 0, return an empty string
• repr() should return a string representation of the rectangle to be able to recreate a new instance by using eval() (see example below)
• Print the message Bye rectangle... (... being 3 dots not ellipsis) when an instance of Rectangle is deleted
• Static method def bigger_or_equal(rect_1, rect_2): that returns the biggest rectangle based on the area
  • rect_1 must be an instance of Rectangle, otherwise raise a TypeError exception with the message rect_1 must be an instance of Rectangle
  • rect_2 must be an instance of Rectangle, otherwise raise a TypeError exception with the message rect_2 must be an instance of Rectangle
  • Returns rect_1 if both have the same area value
• Class method def square(cls, size=0): that returns a new Rectangle instance with width == height == size
• You are not allowed to import any module

guillaume@ubuntu:~/0x08$ cat 9-main.py
#!/usr/bin/python3
Rectangle = __import__('9-rectangle').Rectangle

my_square = Rectangle.square(5)
print("Area: {} - Perimeter: {}".format(my_square.area(), my_square.perimeter()))
print(my_square)

guillaume@ubuntu:~/0x08$ ./9-main.py
Area: 25 - Perimeter: 20
#####
#####
#####
#####
#####
Bye rectangle...
guillaume@ubuntu:~/0x08$

No test cases needed

10. N queens

Chess grandmaster Judit Polgár, the strongest female chess player of all time

The N queens puzzle is the challenge of placing N non-attacking queens on an N×N chessboard. Write a program that solves the N queens problem.

• Usage: nqueens N
  • If the user called the program with the wrong number of arguments, print Usage: nqueens N, followed by a new line, and exit with the status 1
• where N must be an integer greater or equal to 4
  • If N is not an integer, print N must be a number, followed by a new line, and exit with the status 1
  • If N is smaller than 4, print N must be at least 4, followed by a new line, and exit with the status 1
• The program should print every possible solution to the problem
  • One solution per line
  • Format: see example
  • You don’t have to print the solutions in a specific order
• You are only allowed to import the sys module

Read: Queen, Backtracking

julien@ubuntu:~/0x08. N Queens$ ./101-nqueens.py 4
[[0, 1], [1, 3], [2, 0], [3, 2]]
[[0, 2], [1, 0], [2, 3], [3, 1]]
julien@ubuntu:~/0x08. N Queens$ ./101-nqueens.py 6
[[0, 1], [1, 3], [2, 5], [3, 0], [4, 2], [5, 4]]
[[0, 2], [1, 5], [2, 1], [3, 4], [4, 0], [5, 3]]
[[0, 3], [1, 0], [2, 4], [3, 1], [4, 5], [5, 2]]
[[0, 4], [1, 2], [2, 0], [3, 5], [4, 3], [5, 1]]
julien@ubuntu:~/0x08. N Queens$