Quiz 5b#

Question 1#

Which of the following expressions corresponds to a dictionary with no elements?

()
dict()
{}
<>
None
[] \

dict() \

Question 2#

Given an existing dictionary favorites, what Python statement adds the key "fruit" to this dictionary with the corresponding value "blackberry"?

favorites["fruit" : "blackberry"]
favorites["fruit"] = "blackberry"
favorites{"fruit" : "blackberry"}
favorites = {"fruit" : "blackberry"}
favorites["fruit" = "blackberry"] \

favorites["fruit"] = "blackberry"

favorites = {"fruit" : "blackberry"} does not add but initialize the dict()

Question 3#

Keys in a dictionary can have which of the following types?

Numbers
Strings
Dictionaries
Lists
Booleans
Tuples \

Numbers
Strings
Booleans
Tuples \

Question 4#

Values in a dictionary can have which of the following types?

Numbers
Dictionaries
Booleans
Strings
Tuples
Lists \

everything!

Values can even be empty:

d = {1: None}

Question 5#

We often want to loop over all the key/value pairs in a dictionary. Assume the variable my_dict stores a dictionary. One way of looping like this is as follows:

for key in my_dict:
    value = my_dict[key]
    #…

However, there is a better way. We can instead write the following:

for key, value in #???:
    #…

What code should replace the question marks so that the two forms are equivalent?

Refer to the video on dictionaries or the CodeSkulptor documentation .

my_dict.keys()
my_dict.items()
items(my_dict)
list(my_dict)
my_dict.values()
my_dict.keys_values() \

my_dict.items() \

Question 6#

Conceptually, the purpose of a dictionary is to represent a relationship between two collections of data — each key in the dictionary is related to one value. Which of the following situations are instances of such a relationship?

Do not include situations where you have to introduce additional information in order to fit them into such a relationship.

Storing x and y coordinates of an arbitrary collection of 2-dimensional points
Storing x and y coordinates of 2-dimensional points taken from a function, so that each x coordinate occurs at most once.
Storing where each person lives
Storing a sensor’s data samples \

Storing x and y coordinates of 2-dimensional points taken from a function, so that each x coordinate occurs at most once.
Storing where each person lives \

Question 7#

In the previous quiz, you were asked to complete the following code:

import random

def random_point():
    """Returns a random point on a 100x100 grid."""
    return (random.randrange(100), random.randrange(100))

def starting_points(players):
    """Returns a list of random points, one for each player."""
    points = []
    for player in players:
        point = random_point()
        # ???
    return points

Now, we want to rewrite starting_points using a list comprehension. Which list comprehensions could replace the following question marks?

def starting_points(players):
    """Returns a list of random points, one for each player."""
    return #???

Refer to this week’s “Visualizing iteration” video for examples of list comprehensions. Also, try each example in CodeSkulptor before answering the question.

[random_point(player) for player in players]
[random_point for player in players]
[random_point() for player in players]
[for player in players: random_point()]
[random_point for players]
[random_point() for p in players] \

[random_point() for player in players]
[random_point() for p in players]

or better if we do not use the iteration variable:

[random_point() for _ in players]

Question 8#

You have the following code. The goal is to display a portion of the image, rescaling it to fill the canvas.

import simplegui

frame_size = [200, 200]
image_size = [1521, 1818]

def draw(canvas):
    canvas.draw_image(image, image_size, 
                     [image_size[0] / 2, image_size[1] / 2], 
                     [frame_size[0] / 2, frame_size[1] / 2], 
                     frame_size)

frame = simplegui.create_frame("test", frame_size[0], frame_size[1])
frame.set_draw_handler(draw)
image = simplegui.load_image("http://commondatastorage.googleapis.com/codeskulptor-assets/gutenberg.jpg")
frame.start()

Run it, and observe that nothing is displayed in the frame. What is the problem?

The file is not an image.
The file doesn’t exist.
One or more of the draw_image arguments are of the wrong type.
The destination arguments in draw_image are incorrect. We aren’t specifying values that would draw the image on this size canvas.
The source arguments in draw_image are incorrect. We are trying to load pixels that are not within the image, and thus the draw fails. \

The source arguments in draw_image are incorrect. We are trying to load pixels that are not within the image, and thus the draw fails. \

Question 9#

Write a CodeSkulptor program that loads and draws the following image:

http://commondatastorage.googleapis.com/codeskulptor-assets/alphatest.png

with a source center of [220, 100] and a source size of [100, 100]. What one word appears in the canvas? If a letter is capitalized in the image, enter it as a capital.

Note that you do have to position the image as stated to see the correct word.

Enter answer here:\

tin

try:
    import simplegui
except ModuleNotFoundError:
    import simplequi as simplegui

ALPHATEST = \
    'http://commondatastorage.googleapis.com/codeskulptor-assets/alphatest.png'


def draw(c: simplegui.Canvas):
    c.draw_image(im, [220, 100], [100, 100], [50, 50], [100, 100])


f = simplegui.create_frame('', 100, 100)
im = simplegui.load_image(ALPHATEST)
f.set_draw_handler(draw)
f.start()

Quiz 5b

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