PS6 Comments

1. (+ 1 1)

   2

   1 + 1
2. (+ (* 2 3) (* 4 5))

   26

      (2 * 3) + (4 * 5)
   

   Note that parentheses are optional, but not necessary here, since the * operator has higher precedence (will bind its operands earlier) than the + operator, so the Python expression 2*3+4*5 means what we think it should mathematically.
3. (define (square x) (* x x))

     def square(x): return x*x
   

4. (square 4)

   16

      square(4)
   

5. (if (> 3 4) 5 6)

   6

   if 3 > 4:
      5
   else:
      6
   

Question 2: By examining the code in adventure.py and understanding what it means to inherit methods in subclasses, explain what happens when:

1. The is_ownable method is invoked on a OwnableObject.
   The OwnableObject class defines a method,

       def is_ownable(self): return True
   

   so when is_ownable() is invoked on an OwnableObject, the result is True.
2. The is_ownable method is invoked on a MobileObject.
   The MobileObject class does not define an is_ownable method, so when is_ownable() is invoked on a MobileObject, the superclass method is called. The superclass of MobileObject is PhysicalObject. The PhysicalObject class also does not define the is_ownable method, so we look to its superclass, SimObject. This implements the method,

       def is_ownable(self):
           return False # overridden by some subtypes
   

   so the result of is_ownable() when invoked on a MobileObject is False.

class Professor (Lecturer):
	def profess(self, s):
	    self.lecture("It is intuitively obvious that " + s)

        self.say("It is intuitively obvious that " + s + " - you should be taking notes")

class Dean (Professor):
   def say(self, s):
       Professor.say(self, s + " Please give money, we are in debt!")

Some of the students in Charlottansville have a strange habit of getting undressed and running around the Green, so the Student class needs an instance variable dressed that indicates whether or not the student is clothed. Initially, all students are dressed, so the dressed variable is initialized to True. So, your Student class needs to override the __init__ constructor, similarly to how the Person class overrides the __init__ constructor of MobileObject.

In addition, your Student class should implement three methods:

• get_undressed(self) — If the object is already undressed, it should say something about having no more clothes to remove. Otherwise, change the state of dressed to False. (In Scheme, we would name this method get-undressed! with an exclamation point to indicate that the method is a mutator since it changes the state of the self object. Python does not allow ! to be used in names, so we cannot include one in the method name, event though depending on the current location of the student, it may be appropriate to have more than one exclamation point here.) The undressed student should also say "Brr! It's cold!" (or something more creative, but not less tasteful).
• get_dressed(self) — changes the state of dressed to True. If the student was undressed, the student should say "I feel much better now.".
• is_dressed(self) — evaluates to True if the student is dressed and False otherwise.

class Student(Person):
    def __init__(self, name):
        Person.__init__(self, name)
        self.dressed = True

    def get_undressed(self):
        if is_dressed():
            self.dressed = False
            self.say("Brr! It's cold!")
        else:
            self.say("I have nothing left to remove!")

    def get_dressed(self):
        if !is_dressed:
            self.say("I feel much better now.")
            self.dressed = True
        else:
            self.say("I'm already dressed, thank you.");

    def is_dressed(self):
        return self.dressed

    def arrest(self, person):
        if self.location != person.location:
            self.say("I cannot arrest " + person.name + " because she is at " + person.location.name)
        else:
            self.say(person.name + ", you are under arrest!)
            self.say("You have the right to remain silent, call methods, and mutate state.")
            person.move(self._jail)

    def tick(self):
        foundAny = False
        for p in self.location.get_things():
            if isinstance(p, Student):
                if not p.is_dressed():
                    foundAny = True
                    self.arrest(p)
        if not foundAny:
            self.say("No one to arrest here")
            Person.tick(self)

    def tick(self):
        students = filter(lambda s: isinstance(s, Student), self.location.get_things())
        undressedstudents = filter(lambda t: t.is_dressed() == False, students)
        if len(undressedstudents) == 0:
            self.say("Its lonely here...")
            Person.tick(self)
        else:
            map(lambda undressedstudent: self.arrest(undressedstudent), undressedstudents)

    def tick(self):
        streakers = filter(lambda s: isinstance(s, Student) and s.is_dressed(), 
                    	   self.location.get_things())
        if len(streakers) == 0:
            self.say("Its lonely here...")
            Person.tick(self)
        else:
            map(lambda s: self.arrest(s), streakers)

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