Python data structures (lists, dicts) quiz

Question 1

What is a Python list, and why is it useful for storing data in AI projects?

Accepted Answer

An ordered collection of items that can be accessed by position

Answer

A single value stored in memory

Answer

A collection where every item must be a number

Answer

A fixed-size collection that cannot be changed

Question 2

What is a Python dictionary, and how is it different from a list?

Accepted Answer

A collection of key-value pairs where items are accessed by a label

Answer

A list that is sorted alphabetically

Answer

A collection that stores items only as numbers

Answer

An ordered sequence accessed by position number

Question 3

If scores = [85, 92, 78, 90], what does scores[0] return?

Accepted Answer

85

Answer

92

Answer

78

Answer

1

Question 4

Which method adds a new item to the end of a Python list?

Accepted Answer

.append()

Answer

.add()

Answer

.insert()

Answer

.push()

Question 5

How do you find the number of items in a Python list?

Accepted Answer

len(list)

Answer

list.count()

Answer

list.size()

Answer

count(list)

Question 6

In AI, datasets are often stored as lists of numbers called feature vectors. If features = [height, weight, age], what does features[1] represent?

Accepted Answer

weight

Answer

height

Answer

age

Answer

The length of the list

Question 7

How do you access the value associated with a key in a Python dictionary?

Accepted Answer

animal["legs"]

Answer

animal.legs

Answer

animal[0]

Answer

animal("legs")

Question 8

What does the following code print?

labels = ["cat", "dog", "cat", "fish", "dog", "dog"]
counts = {}
for label in labels:
    if label in counts:
        counts[label] += 1
    else:
        counts[label] = 1
print(counts)

Accepted Answer

{'cat': 2, 'dog': 3, 'fish': 1}

Answer

{'cat': 1, 'dog': 1, 'fish': 1}

Answer

{'cat': 3, 'dog': 2, 'fish': 1}

Answer

[2, 3, 1]

Question 9

Which of the following correctly creates a Python dictionary to store a student's test scores by subject?

Accepted Answer

{"math": 90, "science": 85, "english": 78}

Answer

["math": 90, "science": 85]

Answer

{"math", 90, "science", 85}

Answer

dict["math"=90, "science"=85]

Question 10

What is list slicing, and how can it be used to split a dataset into training and testing sets?

Accepted Answer

It extracts a portion of a list between two indices

Answer

It reverses a list

Answer

It creates a full copy of a list

Answer

It removes duplicate items from a list

Question 11

What is a list comprehension, and how does it help preprocess data quickly in AI?

Accepted Answer

A one-line syntax to build a new list by transforming each item

Answer

A method to sort a list in place

Answer

A way to search for a specific item in a list

Answer

A function that removes duplicates from a list

Question 12

A dataset is stored as a list of dictionaries. What does dataset[1]["label"] return?

dataset = [
    {"feature": 5.1, "label": "setosa"},
    {"feature": 6.3, "label": "versicolor"},
    {"feature": 4.9, "label": "setosa"},
]

Accepted Answer

"versicolor"

Answer

"setosa"

Answer

6.3

Answer

1

Question 13

Why might an AI engineer prefer a Python dictionary over a list when storing word frequencies for a text classification model?

Accepted Answer

Dictionaries allow instant lookup by word (key), while lists require scanning each item

Answer

Dictionaries use less memory than lists

Answer

Dictionaries automatically sort words alphabetically

Answer

Lists cannot store strings, only numbers

Question 14

What does the .get() method on a dictionary do, and why is it safer than direct key access with square brackets?

Accepted Answer

It returns the value for a key or a safe default if the key does not exist

Answer

It adds a new key to the dictionary

Answer

It deletes a key from the dictionary

Answer

It returns a list of all keys

Question 15

How can you use Python's zip() function with two lists to create a dictionary mapping feature names to values?

Accepted Answer

zip() pairs items from two lists; dict(zip(...)) makes a dictionary from those pairs

Answer

zip() merges two lists into one flat list

Answer

zip() removes items shared between two lists

Answer

zip() creates a list of sums of corresponding items

Question 16

What is the difference between list.sort() and sorted(list) in Python?

Accepted Answer

sort() modifies the original list in place; sorted() returns a new sorted list

Answer

They are identical in behavior

Answer

sort() returns a new list; sorted() modifies the original

Answer

sorted() only works on lists of numbers

Question 17

In a machine learning pipeline, how could you use a dictionary to perform label encoding — converting text category labels into numbers?

Accepted Answer

Use a dict mapping each category string to a unique integer, then replace labels via the dict

Answer

Store all labels as floating-point values

Answer

Sort the labels alphabetically and assign ranks

Answer

Count how many times each label appears

Question 18

What is a nested dictionary in Python, and how could it represent a small AI dataset with multiple features per sample?

Accepted Answer

A dictionary where some values are themselves dictionaries

Answer

A dictionary with only numeric keys

Answer

A list stored inside a dictionary value

Answer

A dictionary that is automatically sorted by its values

Question 19

You want to build a vocabulary for an NLP model. Given a list of words, how would you create a dictionary mapping each unique word to a unique index number?

Accepted Answer

Loop through words and assign each new word the next available index using len(vocab)

Answer

Use sorted() to sort the words and assign indices based on alphabetical order

Answer

Create a list of all words including duplicates and use list indices directly

Answer

Split the list into equal halves and number each half separately

Question 20

Which dictionary method lets you loop through all key-value pairs at the same time in a for loop?

Accepted Answer

.items()

Answer

.keys()

Answer

.values()

Answer

.pairs()

Question 21

An AI model outputs a list of predicted class probabilities: probs = [0.1, 0.7, 0.2]. How would you find the index of the highest probability using Python?

Accepted Answer

probs.index(max(probs))

Answer

probs.max()

Answer

max(probs)

Answer

probs.sort()[-1]

Question 22

What is the difference between copying a list with new = old versus new = old[:] in Python?

Accepted Answer

new = old makes both variables point to the same list; new = old[:] creates a separate copy

Answer

Both create independent copies of the list

Answer

new = old creates a copy; new = old[:] creates a reference

Answer

new = old[:] is slower but produces the same result as new = old

Question 23

How can you use a Python dictionary to detect and count duplicate items in a list, and why is this useful in data cleaning?

Accepted Answer

Use a dictionary to count occurrences; keys with count > 1 are duplicates

Answer

Sort the list and compare adjacent items

Answer

Subtract one list from another to find shared items

Answer

Use the .duplicate() method available on Python lists

Question 24

What does the following one-hot encoding code produce, and why is one-hot encoding used in AI?

classes = ["cat", "dog", "fish"]
one_hot = {c: [1 if c == cls else 0 for cls in classes] for c in classes}

Accepted Answer

{"cat": [1, 0, 0], "dog": [0, 1, 0], "fish": [0, 0, 1]}

Answer

{"cat": 1, "dog": 2, "fish": 3}

Answer

[[1,0,0],[0,1,0],[0,0,1]]

Answer

{"cat": [0, 1, 1], "dog": [1, 0, 1], "fish": [1, 1, 0]}

Question 25

How is a Python dictionary related to the JSON data format, and why does this matter for AI applications?

Accepted Answer

Python dictionaries and JSON objects share very similar key-value syntax and convert easily between each other

Answer

JSON and Python lists have identical syntax; dicts are unrelated

Answer

JSON can only store numbers, while Python dicts store strings

Answer

Python dicts must be converted to lists before being saved as JSON

Question 26

What happens when you try to access a key in a Python dictionary that does not exist using square bracket notation?

Accepted Answer

It raises a KeyError and stops the program

Answer

It returns 0

Answer

It returns None silently

Answer

It automatically adds the key with a value of None

Question 27

What does list(my_dict.keys()) return, and how could you use it in a machine learning context?

Accepted Answer

A list of all keys in the dictionary

Answer

A list of all values in the dictionary

Answer

A list of all key-value pairs as tuples

Answer

The number of keys in the dictionary

Question 28

Why is looking up a value in a Python dictionary much faster than searching for a value in a Python list, especially as data grows larger?

Accepted Answer

Dictionaries use hashing to find values in near-constant time, while lists require scanning each item

Answer

Dictionaries sort their keys so binary search can be used

Answer

Lists store data in slower disk memory while dicts use RAM

Answer

Python automatically speeds up dictionaries using extra hardware

Question 29

How do you remove a key-value pair from a Python dictionary, and why might you need to do this in a data preprocessing step?

Accepted Answer

del record["name"] or record.pop("name")

Answer

record.remove("name")

Answer

record["name"] = None

Answer

record.delete("name")

Question 30

What will the following code output, and what does this reveal about negative indexing in Python lists?

words = ["AI", "learns", "from", "data"]
print(words[-1])
print(words[-2])

Accepted Answer

"data" and "from"

Answer

"AI" and "learns"

Answer

An error, because negative indices are not allowed

Answer

"from" and "learns"

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