03 Data Structures

Question 1

What kinds of data structures did we learn of?

Answer 1

• sequence types
• unordered collections
• mapping types

Question 2

What are sequence types of data structures?

Answer 2

It’s an ordered list of values where the position/index of the values is used to access them.
ie: list, tuple, string, range

Question 3

What are unordered collections?

Answer 3

unordered set of unique elements.
ie: set

Question 4

What are mapping types of data structures?

Answer 4

It’s a group of key-value-pairs where unique keys are used to access their values.
ie: dictionary

Question 5

What is the difference between a list and a tuple?

Answer 5

A list is mutable (can be changed), a tuple is immutable (can’t be changed).

(everytime a tuple is changed a new tuple with the same name is created and the old one gets deleted.)

Question 6

True or False: in Python, a list only contains a group of values of the same type.

Answer 6

False. It can contain items of variable data types.

Question 7

True or False: The order of items in a list is preserved.

Answer 7

True

Question 8

How is a list created?

Answer 8

Using square brackets containing comma-separated values.

ie: my_list = [0, 5.5, “string”, 8]

Question 9

True or False: in Python, a list contains a group of values of various type.

Answer 9

True

Question 10

How are tuples created?

Answer 10

Via a number of values separated by commas.
ie: my_tuple = 0, 5.5, “string”, 8
or: my_tuple = (0, 5.5, “string”, 8)

Question 11

How is an empty set created?

Answer 11

By using the method set().
ie: my_set = set()

Question 12

How is a set with at least one element created?

Answer 12

By using curly braces and comma separated values.
ie: my_set = {0, 5.5, “string”, 8}

Question 13

What are the values in set3?

set1 = {1, 2, 3}
set2 = {3, 4, 5}
set3 = set1 & set2

Answer 13

{3}

Question 14

What are the values in set3?

set1 = {1, 2, 3}
set2 = {3, 4, 5}
set3 = set1 | set2

Answer 14

{1, 2, 3, 4, 5}q

Question 15

What are the values in set3?

set1 = {1, 2, 3}
set2 = {3, 4, 5}
set3 = set1 - set2

Answer 15

{1, 2}

Question 16

Which of the following statement/s is/are correct?

1. Dictionaries are immutable and unordered.
2. Dictionaries are mutable and unordered.
3. Dictionaries are mutable and ordered.
4. Dictionaries are immutable and ordered.

Answer 16

3 is correct.

Question 17

In Python dictionaries, what can be used as keys?

Answer 17

any hashable object

Question 18

In Python dictionaries, what can be used as values?

Answer 18

any object

Question 19

How are dictionaries created?

Answer 19

my_dict = {key1: value1, key2: value2}
or
my_dict = dict(key1=value1, key2=value2)

Question 20

What’s the output of these statements?

my_dict = dict(1=”starter”, 2=”main”, 3=”dessert”)
my_dict[1] = “soup”
print(my_dict)

Answer 20

Error in line 2

When creating a dictionary using the dict() function, the keys are automatically converted to strings. So getting the value of key 1 isn’t possible. Only the value of key “1” can be accessed.

Question 21

What’s the output of these statements?

my_dict = dict(1=”starter”, 2=”main”, 3=”dessert”)
my_dict[“1”] = “soup”
print(my_dict)

Answer 21

{“1”: “soup”, “2”: “main”, “3”: “dessert”}

Because when creating a dictionary using the dict() function, the keys are automatically converted to strings.
With the second statement the value of key “1” is changed from “starter” to “soup”.

Question 22

What’s the output of these statements?

my_dict = dict(1=”starter”, 2=”main”, 3=”dessert”)
my_dict = {1: “starter”}
print(my_dict)

Answer 22

{1: “starter”}

In line 1 the dictionary is created and in line 2 it is overwritten. This time the creation is done with curly braces so the keys stay the same data type, in this case an integer.

Question 23

What’s the output of these statements?

my_dict = {1=”starter”, 2=”main”, 3=”dessert”}
my_dict[“8”] = “cheese”
print(my_dict)

Answer 23

{1: “starter”, 2: “main”, 3: “dessert”, “8”: “cheese”}

In line 1 the creation is done with curly braces so the keys stay the same data type, in this case an integer.
Then, in line 2, a new entry is added but this time the key is a string.

Question 24

What’s the output of these statements?

my_dict = dict(1=”starter”, 2=”main”, 3=”dessert”)
soup = my_dict[“1”]
print(my_dict)

Answer 24

{“1”: “starter”, “2”: “main”, “3”: “dessert”}

In line 1 the creation is done using the dict() function so the keys are automatically converted to keys.
In line 2 the value of key “1” is saved to a variable “soup”.
The dictionary is still the same as when it was created, it hasn’t changed.

Question 25

What is List Comprehension?

Answer 25

A compact way to loop over an inerable, optionally execute actions on each element and store the results in a list. It can also optionally include conditions to filter the elements for which the actions should be executed.

Question 26

What is the syntax for a list comprehension that includes actions and a condition?

Answer 26

new_list = [code-to-be-executed for element in iterable if condition]

Question 27

What is slicing, what is its syntax and what are its default values?

Answer 27

It’s a way to select a range of items in a sequence (ie in a list, in a string, in a set,…).

Syntax:
sequence[start:end:step]

Default values:
start: 0 (inclusive)
end: length of sequence (exclusive)
step: 1

Question 28

What’s the output of these statements?

my_list = [1, 2, 3, 4, 5]

1. print(my_list[2:4:1])
2. print(my_list[1:4])
3. print(my_list[:4:3])
4. print(my_list[0::2])
5. print(my_list[::-1])

Answer 28

1. [3, 4, 5]
2. [2, 3, 4] (step default value is 1)
3. [3] (start default value is 0)
4. [2, 4] (end default value is last item)
5. [5, 4, 3, 2, 1] (negativ step = reverse order)

Question 29

What does unpacking of a sequence mean?

Answer 29

Assigning the values of a sequence to a series of variables.