Python List Slicing and Step Values

A timeline report extracts recent entries and a reversed view.

What You Need to Understand

List slicing with [start:stop:step] creates a new list using a half-open interval: start is included and stop is excluded. A negative step traverses backward.

When to Use It

A timeline report extracts recent entries and a reversed view.

Step-by-Step Python Example

days = ["Mon", "Tue", "Wed", "Thu", "Fri"]
print(days[1:4])
print(days[::2])
print(days[::-1])

How the Example Works

The first slice selects Tuesday through Thursday; the second skips every other entry; the third reverses the sequence.

Example Output

['Tue', 'Wed', 'Thu']
['Mon', 'Wed', 'Fri']
['Fri', 'Thu', 'Wed', 'Tue', 'Mon']
[4, 5, 6]

A Second Example

Compare this smaller variation with the main example, then experiment with your own values.

numbers = [1, 2, 3, 4, 5, 6]
print(numbers[-3:])

Important Behavior and Edge Cases

A zero step raises ValueError. Unlike single-element indexing, slicing outside boundaries does not normally raise IndexError.

Try It Yourself

Select the final three elements from a list with at least five entries.

Common Beginner Mistakes

A zero step raises ValueError. Unlike single-element indexing, slicing outside boundaries does not normally raise IndexError.
Assuming every sequence operation modifies the original data or that a tuple makes nested mutable objects immutable.

Key Takeaways

List slicing with [start:stop:step] creates a new list using a half-open interval: start is included and stop is excluded.
The first slice selects Tuesday through Thursday; the second skips every other entry; the third reverses the sequence.
A zero step raises ValueError.