access_modifiers_composition_design.md

Lesson: Access Modifiers, Composition & Design

📝  Class Materials:

• Slides

• Repls:

  • Coding Exercise 1:

#In this example we will walk through how different access modifiers are indicated in Python
class Snake:
  def __init__(self, name, color, type):
    #public property
    self.name = name

    #protected
    self._color = color

    #private
    self.__type = type

  def example1(self):
    print("I eat rodents! (This is public)")

  def _example2(self):
    print("I like to slither in the sand (This is protected)")
    self.__example3()

  def __example3(self):
    print("I like to curl up on a hot rock! (This is private)")

# Make a snek caled albert
albert = Snake("Albert", "yellow", "Python")

# Look at each line below. Predict the output 
# by examining the class above. Then uncomment 
# the line and run the code: 

# albert.__example3()
# albert.example1()
# albert._example2()
# print(albert.name)
# print(albert._color)
# print(albert._Snake__type)
# print( dir(albert) )

• Coding Exercise 2:

# Make a class that creates an instance of yourself! 
# Your class will have some public, protected, and 
# private attributes. 

#TODO: Create a class that desribes you! Give your class three attributes

#TODO: Give your class one private, one protected, and one public attribute

#TODO: Give you class one private, one protected, and one public method

# TODO: Instantiate your class and try to modify each attribute

• Coding Exercise 3:

# In this example we will show how to create getters and setters for properties within a class

class Person:
  """This class represents a person with a name, and age"""

  def __init__(self, name, age):
    """Initializes the Person class"""
    self.__name = name
    self.__age = age

  def get_name(self):
    """This method returns the name plus the prefix text"""
    return "The person's name is: " + self.__name

  def set_name(self, new_name):
    self.__name = new_name

  def set_age(self, new_age):
    if new_age > 0:
      self.__age = new_age
    else:
      print("error")

  def get_age(self):
    return self.__age


jess = Person("Jess", 29)
name = jess.get_name()
print(name)
name = "Bob"

print(jess.get_name())
jess.set_name("Bob")
print(jess.get_name())

jess.set_age(40)
print(jess.get_age())
jess.set_age(-1)
print(jess.get_age())

• Coding Exercise 4: https://repl.it/@MakeSchool/composition#main.py

# Let's create a Player and then a Team class using composition!

class Player:
  def __init__(self, name, number):
    self.name = name
    self.number = number
    self.team = None
  
  def intro(self):
    print(f"Name: {self.name} number: {self.number} team: {self.team.name}")


class Team:
  def __init__(self, name, city, num_players):
    self.name = name
    self.city = city
    self.players = []
    self.num_players = num_players

  def add_player(self, player):
    player.team = self
    self.players.append(player)

  def roster(self):
    for player in self.players:
      print(player.name)


myTeam = Team("CS1.1", "San Francisco", 13)
andy = Player("Andy", 6)
myTeam.add_player(andy)

bob = Player("Bob", 7)
myTeam.add_player(bob)

myTeam.roster()

andy.intro() # andy says their name, number and team. 

# Both player and Team are classes. 
# Team has a list of players. 
# A Team is not a Player is not a Team!

# Note! Team owns a list of PLayers. Team can communicate 
# with Player in the the list. See the roster method. 

# On the other hand Player has no way to to communicate 
# with its Team. That is unless we provide that mechanism!

# Look at the Player's team attribute. Look at the the 
# Team's add_player method. Here, each time a player is 
# added to the team that players team attribute is set 
# to the team object. 

Challenge!

You need to create two classes. One will represent a playing card. The other will represent a deck of cards.

A deck of cards has 52 cards in four suits and two colors. Suits are:

• ♠️ Spades
• ♣️ Clubs
• ♥️ Hearts
• ♦️ Diamonds

Values range from 1-13.

Stretch challenge values range from Ace, 2-10, Jack, Jack, Queen, King.

Color is either Red for Hearts and Diamonds, or black for Spades and Clubs.

Card class will have attributes of:

• suit - The suit
• value - the value
• color - the color

Card will also have a show() method that prints the value and suit.

Deck class will have attributes of:

• cards - a list of Card instances

Deck will have methods of:

• add_card() - populates the cards list with cards.
• shuffle() - randomzies the list of cards. Note! You can use random.shuffle() from the built in python library.

Stretch Challenges

• Add a draw() method to the Deck class. This method returns the first card in the cards list and returns it.
• Add a discard_pile attribute to the Deck class. This property is a list that holds cards that were discarded.
• Add a discard() method that takes a card and adds it to the discard list.
• Every card should know what deck it belongs to. Add a deck attribute to the Card class. When a card is created set it's deck to the deck that created it.
• Give Card a discard method. This method should add that card to it's deck's discard pile. A card can call discard on it's deck and pass it self as an argument!
• Create a Hand class. A had class is like a small deck. It stores a list of cards in an attribute. It also has a deck attribute that is the deck that the hand was drawn from.
• Add a draw_hand() method to the Deck class. This method should return a new instance of the Hand class and populate it with 7 cards.
• The Hand class needs a draw method. This method calls draw on the deck the hand is working with and adds the returned card to the hand's cards list.
• Hand should have a show() method. This method displays the cards in a hand by printing them. You can call the show() method on each card in the hand's cards list.
• A Hand needs a discard_random() method. This method chooses a random card in the hand's cards list and passes it to it's deck's discard method.
• Add a discard() method to the Hand class. This method takes the index of a card in the cards list and discards that card.