Python range() Function

The range() function is one of the most commonly used built-in functions in Python. It is mainly used with the for loop to generate a sequence of numbers. Instead of writing numbers manually, the range() function automatically generates them according to the specified start, stop, and step values.

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Learning Objectives

• Understand the purpose of the range() function.
• Learn different forms of the range() function.
• Generate sequences using start, stop, and step values.
• Use positive and negative step values.
• Write programs using the range() function.

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What is range()?

The range() function generates a sequence of integers. It is commonly used in loops where a block of code needs to execute a specific number of times.

The numbers generated by range() are:

• Ordered
• Immutable
• Generated one at a time
• Stop before the ending value

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Syntax

1. range(stop)

range(stop)

2. range(start, stop)

range(start, stop)

3. range(start, stop, step)

range(start, stop, step)

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Parameters

Parameter	Description
start	Starting value of the sequence (default = 0)
stop	Ending value (not included in the sequence)
step	Difference between consecutive numbers (default = 1)

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Important Note

The stop value is never included in the generated sequence.

Example:

range(5)

Generated Values

0 1 2 3 4

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Form 1: range(stop)

When only one argument is supplied, Python assumes the starting value as 0 and increments by 1.

Example

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

Output

0
1
2
3
4

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Form 2: range(start, stop)

This form specifies both the starting and ending values. The ending value is not included.

Example

for i in range(3,8):
    print(i)

Output

3
4
5
6
7

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Form 3: range(start, stop, step)

This form specifies the starting value, ending value, and increment/decrement value.

Example

for i in range(2,11,2):
    print(i)

Output

2
4
6
8
10

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Using Negative Step

A negative step generates the sequence in reverse order.

Example

for i in range(10,0,-2):
    print(i)

Output

10
8
6
4
2

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Example 1: Print Numbers from 1 to 10

for i in range(1,11):
    print(i)

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Example 2: Print Even Numbers

for i in range(2,21,2):
    print(i)

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Example 3: Print Odd Numbers

for i in range(1,20,2):
    print(i)

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Example 4: Reverse Counting

for i in range(10,0,-1):
    print(i)

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Example 5: Multiples of 5

for i in range(5,51,5):
    print(i)

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Dry Run

Program

for i in range(2,8,2):
    print(i)

Iteration	Value of i	Output
1	2	2
2	4	4
3	6	6

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Real-Life Applications

• Generating serial numbers.
• Printing multiplication tables.
• Displaying roll numbers.
• Processing fixed number of records.
• Generating calendars and schedules.
• Creating menus and reports.

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Common Programming Mistakes

1. Assuming the Stop Value is Included

Wrong Expectation

range(1,5)

Many beginners expect the output to be:

1 2 3 4 5

Actual Output

1 2 3 4

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2. Incorrect Step Direction

Wrong

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

Explanation: No output is produced because the step is negative while the stop value is greater than the start value.

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3. Step Value Cannot be Zero

Wrong

range(1,10,0)

Explanation: Python raises a ValueError because the step cannot be zero.

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CBSE Important Programs

1. Print numbers from 1 to 100.
2. Print numbers from 100 to 1.
3. Print even numbers.
4. Print odd numbers.
5. Display multiplication table.
6. Print multiples of 3.
7. Print multiples of 5.
8. Display squares of numbers.
9. Display cubes of numbers.
10. Reverse counting.

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Viva Questions

1. What is the purpose of the range() function?
2. What are the three forms of range()?
3. Is the stop value included?
4. What is the default value of start?
5. What is the default value of step?
6. Can the step value be negative?
7. Can the step value be zero?
8. Can range() be used without a loop?
9. Which loop commonly uses range()?
10. Write the output of range(3).

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Exam Tips

• Remember that the stop value is excluded.
• Use a positive step for increasing sequences and a negative step for decreasing sequences.
• Never use a step value of zero.
• Choose the correct form of range() based on the requirement.
• Practice predicting the output of different range() statements.

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