range()

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

Returns: range object · Updated March 13, 2026 · Built-in Functions

built-in iteration sequence numbers looping

The range() function generates an immutable sequence of integers that is commonly used for looping a specific number of times in for loops. Despite its name, range() is actually a built-in sequence type in Python, not a function. It behaves like a lazy list — it doesn’t store all values in memory but generates them on demand, making it memory-efficient for large sequences.

Syntax

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

Parameters

Parameter	Type	Default	Description
`start`	`int`	`0` (if stop provided)	The starting integer of the sequence. Included in the result.
`stop`	`int`	—	The end of the sequence. This value is not included in the result.
`step`	`int`	`1`	The difference between each number in the sequence. Can be positive or negative, but cannot be zero.

Returns: A range object, which is an immutable sequence type. Convert to a list with list() if you need all values at once, or iterate directly with a for loop.

Raises: ValueError if step is zero.

Examples

Basic usage with stop only

When you provide a single argument, it becomes the stop value, and start defaults to 0:

for i in range(5):
    print(i)
# 0
# 1
# 2
# 3
# 4

Notice that the sequence stops at 4, not 5 — the stop value is exclusive.

Using start and stop

Provide two arguments to specify both the start and end of the sequence:

for i in range(2, 8):
    print(i)
# 2
# 3
# 4
# 5
# 6
# 7

Using step to control increments

The step parameter controls the difference between each number:

for i in range(0, 10, 2):
    print(i)
# 0
# 2
# 4
# 6
# 8

Negative step for reverse sequences

Use a negative step to generate sequences in reverse order:

for i in range(5, 0, -1):
    print(i)
# 5
# 4
# 3
# 2
# 1

Converting to a list

Since range() returns a lazy iterator, convert to a list when you need all values:

numbers = list(range(10))
print(numbers)
# [0, 1, 2, 3, 4, 5, 6, 7, 8, 9]

Common Patterns

Looping a specific number of times

The most common use case is repeating an action a fixed number of times:

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

Iterating with index

Combine range() with len() to get both index and value when iterating:

fruits = ["apple", "banana", "cherry"]

for i in range(len(fruits)):
    print(f"{i}: {fruits[i]}")
# 0: apple
# 1: banana
# 2: cherry

Note: In modern Python, enumerate() is often preferred for this pattern as it’s more readable.

Creating padded sequences

Use range() to generate indices for padding or alignment:

# Create a list of zeros with a specific length
zeros = [0] * 5  # This creates [0, 0, 0, 0, 0]

# Or for padding values
indexed_values = [(i, 0) for i in range(5)]
print(indexed_values)
# [(0, 0), (1, 0), (2, 0), (3, 0), (4, 0)]

Skipping elements in a sequence

Use step values greater than 1 to process every nth item:

data = [10, 20, 30, 40, 50, 60, 70, 80, 90, 100]

# Process every 3rd element
for i in range(0, len(data), 3):
    print(f"Index {i}: {data[i]}")
# Index 0: 10
# Index 3: 40
# Index 6: 70
# Index 9: 100

Checking membership efficiently

Since range implements the __contains__ method, checking membership is fast:

if 5 in range(10):
    print("Found it!")
# Found it!

# This is O(1) — much faster than checking a list

Behavior Notes

Empty sequences

If the range would contain no values, you get an empty sequence:

print(list(range(5, 5)))
# []

print(list(range(10, 0, 1)))
# []

Step cannot be zero

Passing step=0 raises a ValueError:

range(0, 10, 0)
# ValueError: range() arg 3 must not be zero

Float arguments not supported

range() only accepts integers. For float sequences, use NumPy’s arange() or a custom implementation:

# This raises TypeError
range(0.5, 2.5)
# TypeError: 'float' object cannot be interpreted as an integer