Data Structures

Question 1

What does the list method append(x) do?

Answer 1

Adds x to the end of the list.

Question 2

What does the list method extend(iterable) do?

Answer 2

Appends all items from an iterable to the list.

Question 3

What does the list method insert(i, x) do?

Answer 3

Inserts x at index i.

Question 4

What does the list method remove(x) do?

Answer 4

Removes the first occurrence of x; raises ValueError if not found.

Question 5

What does the list method pop([i]) do?

Answer 5

Removes and returns item at index i; removes last item if i not given.

Question 6

What does the list method clear() do?

Answer 6

Removes all items from the list.

Question 7

What does the list method index(x[, start[, end]]) do?

Answer 7

Returns the first index of x, optionally within start and end.

Question 8

What does the list method count(x) do?

Answer 8

Counts how many times x appears in the list.

Question 9

What does the list method sort(key=None, reverse=False) do?

Answer 9

Sorts the list in place.

Question 10

What does the list method reverse() do?

Answer 10

Reverses the list in place.

Question 11

What does the list method copy() do?

Answer 11

Returns a shallow copy of the list.

Question 12

Do mutating list methods return a value?

Answer 12

No, they return None.

Question 13

Can lists with mixed incomparable types be sorted?

Answer 13

No, lists with incomparable types cannot be sorted.

Question 14

How can a list act as a stack?

Answer 14

By using append() to push and pop() to pop.

Question 15

Why aren’t lists ideal as queues?

Answer 15

Because pop(0) is inefficient due to element shifting.

Question 16

What should be used for efficient queues?

Answer 16

collections.deque for O(1) operations on both ends.

Question 17

What is a list comprehension?

Answer 17

A concise way to build a new list from an iterable with optional conditions.

Question 18

How does a nested list comprehension work?

Answer 18

It allows an inner comprehension within the expression.

Question 19

What does the del statement do?

Answer 19

Deletes an item, slice, or entire variable without returning a value.

Question 20

What is a tuple?

Answer 20

An immutable, ordered sequence of values separated by commas.

Question 21

Can tuples contain mutable objects?

Answer 21

Yes, tuples can hold mutable objects.

Question 22

How do you define a one-element tuple?

Answer 22

With a trailing comma, e.g. (‘item’,)

Question 23

What is tuple packing?

Answer 23

Assigning multiple values into a single tuple.

Question 24

What is sequence unpacking?

Answer 24

Assigning individual elements of a sequence to separate variables.

Question 25

What is a set in Python?

Answer 25

An unordered collection of unique elements.

Question 26

What are common set operations?

Answer 26

Union, intersection, difference, symmetric difference.

Question 27

How are sets created?

Answer 27

With curly braces or the set() function.

Question 28

Can set comprehensions be used?

Answer 28

Yes, similar to list comprehensions.

Question 29

What is a dictionary in Python?

Answer 29

A collection of key-value pairs with unique, immutable keys.

Question 30

How are dictionaries created?

Answer 30

Using {}, dict(), keyword args, or comprehensions.

Question 31

What happens if you assign a value to an existing key in a dict?

Answer 31

The old value is replaced.

Question 32

What does list(d) return for a dictionary?

Answer 32

A list of keys in insertion order.

Question 33

Can you use dict comprehensions?

Answer 33

Yes, using the format {key: value for ...}.

Question 34

What does dict.items() do?

Answer 34

Returns a view of key-value pairs.

Question 35

What does enumerate() do?

Answer 35

Returns index-value pairs from a sequence.

Question 36

What does zip() do?

Answer 36

Allows iteration over multiple sequences in parallel.

Question 37

What does reversed() do?

Answer 37

Iterates over a sequence in reverse.

Question 38

What does sorted() do?

Answer 38

Returns a sorted version of a sequence.

Question 39

Why avoid modifying a list while iterating?

Answer 39

It can cause unexpected behavior; create a new list instead.

Question 40

What operators can be used in conditions?

Answer 40

in, not in, is, is not, and chained comparisons.

Question 41

What is short-circuit evaluation?

Answer 41

Evaluation stops as soon as the result is determined.

Question 42

What operator allows assignment inside expressions?

Answer 42

The walrus operator :=.

Question 43

How are sequences compared?

Answer 43

Lexicographically, item by item.

Question 44

How are strings compared?

Answer 44

By Unicode code point order.

Question 45

Can mixed numeric types be compared?

Answer 45

Yes, e.g., int with float.

Question 46

What happens when comparing incompatible types?

Answer 46

A TypeError is raised.