Final Exam Practice Problems

As we get closer to the exam, solutions will be posted under Other Content on Blackboard.

What does the following code print?

a = [1, 2, 3, 4]
b = a
b[2] = 6
print('a =', a, 'b =', b)

Using a memory diagram and a couple of sentences, explain the result printed in problem number 1.

What is printed when you invoke prob3() below?

def eat(x):
    x[1] = 9
    x[3] = 11

def prob3():
    food = [4, 5, 6, 7]
    eat(food)
    print('food =', food)

Using a memory diagram and a couple of sentences, explain the result printed in problem number 3.
Write a function create_2d that takes as input two integers height and width, and that creates and returns a 2D list (i.e., a list of lists) with values that are the row number multiplied by the column number. For example:
```
>>> create_2d(3, 5)
[[0, 0, 0, 0, 0], [0, 1, 2, 3, 4], [0, 2, 4, 6, 8]]
```
Write a function add_one that takes an input grid that is a 2D list (a list of lists). Your function should add 1 to each element of grid, but it should not return anything. For example:
```
>>> my_grid = create_2d(3, 5)
>>> add_one(my_grid)
>>> my_grid
[[1, 1, 1, 1, 1], [1, 2, 3, 4, 5], [1, 3, 5, 7, 9]]
```
Create a Python class named Phonebook with a single attribute called entries. Begin by including a constructor that initializes entries to be an empty dictionary.
Next add a method called add_entry that takes a string representing a person’s name and an integer representing the person’s phone number and that adds an entry to the Phonebook object’s dictionary in which the key is the name and the value is the number. For example:
```
>>> book = Phonebook()
>>> book.add_entry('Turing', 6173538919)
```
Add a method named contains to your Phonebook class. It should take a parameter name and return True if name is present in the phonebook, and False otherwise. For example:
```
>>> book = Phonebook()
>>> book.contains('Turing')
False
>>> book.add_entry('Turing', 6173538919)
>>> book.contains('Turing')
True
```
Write another method for your Phonebook class called number_for that takes a parameter name and returns the phone number for name in the called Phonebook object. It should return -1 if name is not found. Here is an example:
```
>>> book = Phonebook()
>>> book.add_entry('Turing', 6173538919)
>>> book.add_entry('Hopper', 6174951000)
>>> book.number_for('Turing')
6173538919
>>> book.number_for('Hopper')
6174951000
>>> book.number_for('Codd')
-1
```
Hint: Consider using your contains method from problem 9!
Create a Python class called Triangle. The constructor for this class should take two arguments, base and height, and store those values in appropriately named attributes. In addition, you should add a method called area that computes and returns the area of the triangle. (The area of a triangle is 0.5 times the product of its base and height.) For example:
```
>>> tri = Triangle(3, 4)
>>> tri.area()
6.0
```
Add a method to your Triangle class that enables you print a Triangle object in a readable way. For example:
```
>>> tri = Triangle(3, 4)
>>> print(tri)
triangle with base 3 and height 4
```
Add a method to your Triangle class that will allow you to use the == operator to test if two Triangle objects are equal–i.e., if they have the same base and height. For example:
```
>>> tri1 = Triangle(3, 4)
>>> tri2 = Triangle(3, 4)
>>> tri3 = Triangle(4, 3)
>>> tri1 == tri2
True
>>> tri1 == tri3
False
```
Write a function called main that creates three triangle objects tri1 (with base 3 and height 4), tri2 (with base 6 and height 6), and tri3 (also with base 3 and height 4). The function should print the three objects and their areas. Next, it should test whether tri1 and tri2 are equal and report the result. Finally, it should test whether tri1 and tri3 are equal and report the result. Your function should take full advantage of the Triangle methods you have written. Here is the desired output:
```
>>> main()
tri1: triangle with base 3 and height 4 (area = 6.0)
tri2: triangle with base 6 and height 6 (area = 18.0)
tri3: triangle with base 3 and height 4 (area = 6.0)
tri1 and tri2 are not equal
tri1 and tri3 are equal
```
Write a subclass of Triangle called EquilateralTriangle. Its constructor should take a single parameter side representing the length of a side. However, the new class should not have any new attributes. Rather, it should use the attributes that are inherited from Triangle, and you should initialize those attributes by calling the superclass constructor and passing it the appropriate values. (You should approximate the height of the triangle as 0.866 times the side length.) For example:
```
>>> tri1 = EquilateralTriangle(6)
>>> print(tri1)
triangle with base 6 and height 5.196
```
Override the appropriate method in EquilateralTriangle so that printing an EquilateralTriangle object produces an output that looks like the following:
```
>>> tri1 = EquilateralTriangle(6)
>>> print(tri1)
equilateral triangle with side 6
```
Construct a deterministic finite state machine that accepts all bit strings that contains three ones in a row – i.e., all bit strings that include the pattern 111 somewhere in the input – and that rejects all other bit strings.