Array Declaration and Initialization in DSA Python - Cheat Sheet & Quick Revision

Recall & Review

beginner

What is an array in simple terms?

An array is like a row of boxes where each box can hold a value. All boxes are the same size and arranged one after another.

beginner

How do you declare an array of 5 integers in Python?

You can declare it using a list like this: arr = [0, 0, 0, 0, 0]. This creates 5 boxes holding 0 initially.

beginner

What does 'initialization' mean when working with arrays?

Initialization means putting starting values into the array boxes right after creating them.

beginner

Show how to declare and initialize an array with values 1, 2, 3, 4, 5 in Python.

Use arr = [1, 2, 3, 4, 5]. This creates an array with 5 boxes holding those numbers.

beginner

Can arrays in Python change size after creation?

Yes, Python lists (arrays) can grow or shrink by adding or removing elements, unlike fixed-size arrays in some other languages.

Which of these is a correct way to declare an array of 3 zeros in Python?

A arr = {0, 0, 0}

B arr = (0, 0, 0)

C arr = [0, 0, 0]

D arr = [0] * 3

Option C creates a list with three zeros. Option A is a set, Option B is a tuple, and D creates a list by repeating 0 three times.

What is the index of the first element in a Python array?

A 1

B 0

C -1

D Depends on the array size

Python arrays (lists) start indexing from 0, so the first element is at index 0.

How do you create an array with values 5, 10, 15 in Python?

A arr = [5, 10, 15]

B arr = (5, 10, 15)

C arr = {5, 10, 15}

D arr = 5, 10, 15

Option A creates a list (array) with the values. B is a tuple, C is a set, and D is a tuple without parentheses.

What happens if you try to access an index outside the array size in Python?

A You get an error

B It returns None

C It returns 0

D It returns the last element

Accessing an index outside the array size causes an IndexError in Python.

Which of these is NOT a way to initialize an array in Python?

A arr = [1, 2, 3]

B arr = list((1, 2, 3))

C arr = {1, 2, 3}

D arr = [0] * 3

Option C creates a set, not a list (array). The others create lists.

Explain how to declare and initialize an array with 4 elements in Python.

Think about using square brackets and putting values inside.

Describe what happens when you try to access an array element by index in Python.

Remember how Python counts positions and what happens if you go too far.