Chapter 9

Question 1

An element in a dictionary has two parts. What are they called?

Answer 1

Key and value

Question 2

Which part of a dictionary element must be immutable?

Answer 2

The key

Question 3

Suppose ‘start’ : 1472 is an element in a dictionary. What is the key? What is the value?

Answer 3

The string ‘start’ is the key, and the integer 1472 is the value.

Question 4

What will the following code display?

stuff = {1 : ‘aaa’, 2 : ‘bbb’, 3 : ‘ccc’}
 print(stuff[3])

Answer 4

ccc

Question 5

Suppose a dictionary named employee has been created. What does the following statement do?

employee[‘id’] = 54321

Answer 5

It stores the key-value pair ‘id’ : 54321 in the employee dictionary.

Question 6

Suppose a dictionary named inventory exists. What does the following statement do?

del inventory[654]

Answer 6

It deletes the element that has the key 654.

Question 7

How can you determine whether a key-value pair exists in a dictionary?

Answer 7

You can use the in operator to test for a specific key.

Question 8

What will the following code display?

stuff = {1 : ‘aaa’, 2 : ‘bbb’, 3 : ‘ccc’}
 print(len(stuff))

Answer 8

3

Question 9

What will the following code display?

stuff = {1 : ‘aaa’, 2 : ‘bbb’, 3 : ‘ccc’}
 for k in stuff:
  print(k)

Answer 9

1
2
3

Question 10

What is the difference between the dictionary methods pop and popitem?

Answer 10

The pop method accepts a key as an argument, returns the value that is associated with that key, and removes that key-value pair from the dictionary.

The popitem method returns a randomly selected key-value pair, as a tuple, and removes that key-value pair from the dictionary.

Question 11

Assume the following list exists:

names = [‘Chris’, ‘Katie’, ‘Joanne’, ‘Kurt’]

Write a statement that uses a dictionary comprehension to create a dictionary in which each element contains a name from the names list as its key, and the length of that name as its value.

Answer 11

result = {item:len(item) for item in names}

Question 11

What does the items method return?

Answer 11

It returns all a dictionary’s keys and their associated values as a sequence of tuples.

Question 12

What does the keys method return?

Answer 12

It returns all the keys in a dictionary as a sequence of tuples.

Question 13

What does the values method return?

Answer 13

It returns all the values in the dictionary as a sequence of tuples.

Question 14

Are the elements of a set ordered or unordered?

Answer 14

Unordered

Question 14

Assume the following dictionary exists:

phonebook = {‘Chris’:’919-555−1111’, ‘Katie’:’828-555−2222’,
 ’Joanne’:’704-555−3333’, ‘Kurt’:’919-555−3333’}

Write a statement that uses a dictionary comprehension to create a second dictionary containing the elements of phonebook that have a value starting with ‘919’.

Answer 14

phonebook_copy = {k:v for k,v in phonebook.items()
if v.startswith(‘919’)}

Question 15

After the following statement executes, what elements will be stored in the myset set?

myset = set(‘Jupiter’)

Answer 15

particular order): ‘J’, ‘u’, ‘p’, ‘i’, ‘t’, ‘e’, and ‘r’.

Question 15

Does a set allow you to store duplicate elements?

Answer 15

No

Question 16

How do you create an empty set?

Answer 16

You call the built-in set function.

Question 17

After the following statement executes, what elements will be stored in the myset set?

myset = set(25)

Answer 17

The set will contain one element: 25.

Question 18

After the following statement executes, what elements will be stored in the myset set?

myset = set(‘www xxx yyy zzz’)

Answer 18

The set will contain these elements (in no particular order): ‘w’, ‘ ‘, ‘x’, ‘y’, and ‘z’.

Question 19

After the following statement executes, what elements will be stored in the myset set?

myset = set([‘www’, ‘xxx’, ‘yyy’, ‘zzz’])

Answer 19

The set will contain these elements (in no particular order): ‘www’, ‘xxx’, ‘yyy’, and ‘zzz’.

Question 19

After the following statement executes, what elements will be stored in the myset set?

myset = set([1, 2, 2, 3, 4, 4, 4])

Answer 19

The set will contain these elements (in no particular order): 1, 2, 3, and 4.

Question 20

How do you determine the number of elements in a set?

Answer 20

You pass the set as an argument to the len function.

Question 21

After the following statement executes, what elements will be stored in the myset set?

myset = set([10, 9, 8])
 myset.update([1, 2, 3])

Answer 21

The set will contain these elements (in no particular order): 10, 9, 8, 1, 2, and 3.

Question 22

After the following statement executes, what elements will be stored in the myset set?

myset = set([10, 9, 8])
 myset.update(‘abc’)

Answer 22

The set will contain these elements (in no particular order): 10, 9, 8, ‘a’, ‘b’, and ‘c’.

Question 22

What is the difference between the remove and discard methods?

Answer 22

If the specified element to delete is not in the set, the remove method raises a KeyError exception, but the discard method does not raise an exception.

Question 23

After the following code executes, what elements will be members of set3?

set1 = set([1, 2, 3, 4])
 set2 = set([3, 4, 5, 6])
 set3 = set1.intersection(set2)

Answer 23

{3, 4}

Question 23

How can you determine whether a specific element exists in a set?

Answer 23

You can use the in operator to test for the element.

Question 24

After the following code executes, what elements will be members of set3?

set1 = set([10, 20, 30])
 set2 = set([100, 200, 300])
 set3 = set1.union(set2)

Answer 24

{10, 20, 30, 100, 200, 300}

Question 25

After the following code executes, what elements will be members of set3?

set1 = set([1, 2, 3, 4])
 set2 = set([3, 4, 5, 6])
 set3 = set1.difference(set2)

Answer 25

{1, 2}

Question 26

After the following code executes, what elements will be members of set3?

set1 = set([1, 2, 3, 4])
 set2 = set([3, 4, 5, 6])
 set3 = set2.difference(set1)

Answer 26

{5, 6}

Question 27

After the following code executes, what elements will be members of set3?

set1 = set([‘a’, ‘b’, ‘c’])
 set2 = set([‘b’, ‘c’, ‘d’])
 set3 = set1.symmetric_difference(set2)

Answer 27

{‘a’, ‘d’}

Question 27

Look at the following code:

set1 = set([1, 2, 3, 4])
 set2 = set([2, 3])

Which of the sets is a subset of the other?

Which of the sets is a superset of the other?

Answer 27

set2 is a subset of set1, and set1 is a superset of set2.

Question 28

What is object serialization?

Answer 28

The process of converting the object to a stream of bytes that can be saved to a file for later retrieval.

Question 29

When you open a file for the purpose of saving a pickled object to it, what file access mode do you use?

Answer 29

‘wb’

Question 30

When you open a file for the purpose of retrieving a pickled object from it, what file access mode do you use?

Answer 30

‘rb’

Question 31

What module do you import if you want to pickle objects?

Answer 31

The pickle module

Question 32

What function do you call to pickle an object?

Answer 32

pickle.dump

Question 33

What function do you call to retrieve and unpickle an object?