slice()

slice(stop) / slice(start, stop[, step])

The slice() function creates a slice object that represents a set of indices for extracting portions of sequences like lists, strings, and tuples. Slice objects are useful when you want to reuse the same slicing operation multiple times or pass slicing parameters to functions.

Syntax

slice(stop)
slice(start, stop)
slice(start, stop, step)

Parameters

Parameter	Type	Default	Description
start	int	None	The starting index of the slice. None means beginning of the sequence.
stop	int	—	The ending index (exclusive). This parameter is required.
step	int	None	The step value. None means step of 1. Negative values reverse the direction.

Examples

Basic usage

my_list = [0, 1, 2, 3, 4, 5, 6, 7, 8, 9]

# Create a slice object
s = slice(5)
print(my_list[s])
# [0, 1, 2, 3, 4]

# Equivalent to my_list[:5]

With start and stop

my_list = [0, 1, 2, 3, 4, 5, 6, 7, 8, 9]

s = slice(1, 5)
print(my_list[s])
# [1, 2, 3, 4]

# Equivalent to my_list[1:5]

With step value

my_list = [0, 1, 2, 3, 4, 5, 6, 7, 8, 9]

s = slice(0, 10, 2)
print(my_list[s])
# [0, 2, 4, 6, 8]

# Equivalent to my_list[0:10:2]

Negative indices

my_list = [0, 1, 2, 3, 4, 5, 6, 7, 8, 9]

# Last three elements
s = slice(-3, None)
print(my_list[s])
# [7, 8, 9]

# Reverse the list
s = slice(None, None, -1)
print(my_list[s])
# [9, 8, 7, 6, 5, 4, 3, 2, 1, 0]

Common Patterns

Reusing slice objects

Create a slice once and use it multiple times:

header = slice(0, 3)
data = ["name", "age", "city", "Alice", "30", "NYC"]

print(data[header])  # ['name', 'age', 'city']
print(data[:3])      # Same result

Passing slices to functions

Slice objects work with any sequence type:

text = "hello world"
s = slice(0, 5)

print(text[s])
# hello

# Works with tuples too
tup = (1, 2, 3, 4, 5)
print(tup[s])
# (1, 2, 3, 4, 5)

Using .indices() method

The .indices() method maps a slice to a concrete range given a sequence length:

s = slice(1, 10, 2)

# For a sequence of length 7
start, stop, step = s.indices(7)
print(f"start={start}, stop={stop}, step={step}")
# start=1, stop=7, step=2

# This tells you which indices would be used
result = list(range(7))[s]
print(result)
# [1, 3, 5]

This is useful when you need to know the actual indices without having the sequence yet, or when working with functions that need to validate slice bounds.

Errors

IndexError with out-of-bounds stop

my_list = [1, 2, 3]
s = slice(0, 10)

try:
    result = my_list[s]
    print(result)  # Still works - Python handles gracefully
except IndexError:
    print("IndexError raised")
# [1, 2, 3] - No error, Python clamps to sequence length

Python is forgiving with slices and does not raise IndexError for out-of-bounds values. It simply clamps to the sequence bounds.

See Also

• range()
• list()
• tuple()