Python range() Function

The range() function in Python is used to generate a sequence of numbers. It's commonly used in for loops to repeat a block of code a specific number of times.

Syntax

range(stop)
range(start, stop)
range(start, stop, step)

Parameters:

• start (optional) – The starting number of the sequence. Defaults to 0.
• stop – The number at which to stop (not included).
• step (optional) – The difference between each number in the sequence. Defaults to 1.

Returns:

An immutable sequence type of numbers.

Example 1: Using range(stop)

for i in range(5):
    print(i)

0
1
2
3
4

Example 2: Using range(start, stop)

for i in range(2, 6):
    print(i)

2
3
4
5

Example 3: Using range(start, stop, step)

for i in range(1, 10, 2):
    print(i)

1
3
5
7
9

Example 4: Reversed Sequence with Negative Step

for i in range(5, 0, -1):
    print(i)

5
4
3
2
1

Use Cases

• Looping over a fixed number of times
• Generating indices for list access
• Iterating in reverse
• Creating sequences for algorithms

Convert to List (for Viewing)

print(list(range(1, 6)))

[1, 2, 3, 4, 5]

Using list() helps you visualize the numbers generated by range().

Common Mistakes

• Forgetting that stop is exclusive (not included)
• Using a step of 0 will raise a ValueError
• Assuming range() returns a list – it returns a special range object

Interview Tip

range() is often used in loop-based questions. Practice customizing start, stop, and step to write optimized code.

Summary

• range() generates numbers from start to stop - 1
• It’s memory-efficient and commonly used in loops
• Convert to list() if you want to view or print the sequence

Practice Problem

Print all even numbers between 10 and 30 using range().

for i in range(10, 31, 2):
    print(i)

10
12
14
16
18
20
22
24
26
28
30