range() Function

The built-in range() function generates an immutable sequence of integers. It is most commonly used with for loops when you need to repeat an action a specific number of times, or when you need a series of numbers such as 0–9, 1–100, or every second number.

for i in range(3):
    print("Hello")

Expected output:

Hello
Hello
Hello

What range() Returns

range() returns an object of its own data type, called range.

r = range(5)
print(r)
print(type(r))

Expected output:

range(0, 5)
<class 'range'>

Two properties make range objects special:

• Immutable — the sequence cannot be changed after it is created. You cannot append, remove, or replace numbers.
• Lazy and memory-efficient — a range does not store every number. It stores only its start, stop, and step, and calculates each number when it is needed. range(1_000_000) uses roughly the same small amount of memory as range(5).

This is why printing a range shows range(0, 5) rather than the numbers themselves.

Syntax

range(start, stop, step)

All three arguments must be integers. range(1.5) raises a TypeError.

Using range() With One Argument

With one argument, the value is the stop value, and the sequence starts at 0.

nums = range(8)
print(list(nums))

Expected output:

[0, 1, 2, 3, 4, 5, 6, 7]

range(8) produces 8 numbers, from 0 to 7. The stop value 8 itself is not included.

Tip: range(n) always produces exactly n numbers. This is why for i in range(n): is the standard way to repeat something n times.

Using range() With Two Arguments

With two arguments, the first is the start and the second is the stop.

nums = range(4, 9)
print(list(nums))

Expected output:

[4, 5, 6, 7, 8]

The sequence begins at 4 (included) and ends at 8 (just before 9). To include a specific end value, set stop one higher — for example, range(1, 11) produces 1 through 10.

Using range() With Three Arguments

The third argument is the step: how much is added to get the next number.

nums = range(2, 15, 3)
print(list(nums))

Expected output:

[2, 5, 8, 11, 14]

Starting at 2, each number is 3 more than the previous one. The next value would be 17, which is not less than 15, so the sequence stops at 14.

Counting Down With a Negative Step

A negative step produces a decreasing sequence. The start must be greater than the stop.

nums = range(10, 0, -2)
print(list(nums))

Expected output:

[10, 8, 6, 4, 2]

The sequence stops before reaching 0.

Empty Ranges

If the start, stop, and step cannot produce any numbers, the range is empty — no error is raised:

print(list(range(5, 2)))

Expected output:

[]

range(5, 2) counts upward by 1 from 5, but 5 is already past 2. To count down, use range(5, 2, -1).

Note: A step of 0 is not allowed: range(1, 5, 0) raises ValueError: range() arg 3 must not be zero.

Using range() in Loops

range() is most often used with for loops.

for number in range(5):
    print("Count:", number)

Expected output:

Count: 0
Count: 1
Count: 2
Count: 3
Count: 4

Practical Example: Multiplication Table

number = 7

for i in range(1, 6):
    print(f"{number} x {i} = {number * i}")

Expected output:

7 x 1 = 7
7 x 2 = 14
7 x 3 = 21
7 x 4 = 28
7 x 5 = 35

Practical Example: Sum of Even Numbers

total = 0

for n in range(2, 11, 2):
    total += n

print("Sum of even numbers from 2 to 10:", total)

Expected output:

Sum of even numbers from 2 to 10: 30

range(2, 11, 2) produces 2, 4, 6, 8, 10. Using a step of 2 is more efficient than checking every number with if n % 2 == 0.

Converting a Range to a List

Because a range does not display its values directly, convert it to a list (or a tuple) to see the full sequence.

print(list(range(3)))
print(list(range(2, 7)))
print(list(range(1, 12, 4)))

Expected output:

[0, 1, 2]
[2, 3, 4, 5, 6]
[1, 5, 9]

Converting creates a real list in memory, so avoid it for very large ranges unless you actually need a list.

Indexing and Slicing Ranges

Ranges are sequences, so they support indexing and slicing just like lists and tuples.

r = range(12)

print(r[4])          # Access a single element
print(r[-1])         # Access the last element
print(r[1:6])        # Slice a range
print(list(r[1:6]))  # View the slice's values

Expected output:

4
11
range(1, 6)
[1, 2, 3, 4, 5]

Note:

• Indexing returns a single integer.
• Slicing returns a new range object, not a list.

Checking Membership With in

Use in to check whether a number belongs to a range.

even_nums = range(0, 20, 2)

print(10 in even_nums)
print(11 in even_nums)

Expected output:

True
False

For integers, this check is very fast: Python calculates the answer mathematically from start, stop, and step instead of looking at every number.

Practical Example: Validating Input Range

age = 25

if age in range(18, 61):
    print("Eligible")
else:
    print("Not eligible")

Expected output:

Eligible

range(18, 61) covers ages 18 through 60. (For whole-number checks this works well; a comparison like 18 <= age <= 60 also handles decimal values.)

Finding the Length of a Range

len() returns how many numbers a range contains.

r = range(1, 20, 3)
print(len(r))
print(list(r))

Expected output:

7
[1, 4, 7, 10, 13, 16, 19]

Common Mistakes

Related Concepts

• Python for Loops — the main place range() is used
• Python Lists — converting ranges into lists
• Python Iterators — how ranges produce values on demand