Slicing

Syntax

sequence[start:stop:step]

Examples

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

print(numbers[2:5])   # [2, 3, 4]  (index 5 is excluded)
print(numbers[:4])    # [0, 1, 2, 3]  (from the start)
print(numbers[6:])    # [6, 7, 8, 9]  (to the end)
print(numbers[:])     # a full copy of the list

text = "Codectionary"

print(text[-1])     # y (last character)
print(text[-4:])    # nary (last four characters)
print(text[:-4])    # Codectio (everything except the last four)

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

print(numbers[::2])   # [0, 2, 4, 6, 8]  (every second item)
print(numbers[1::2])  # [1, 3, 5, 7, 9]  (odd indices)

text = "Python"
print(text[::-1])  # nohtyP

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

Best practices

• Remember the stop index in a slice is exclusive - sequence[2:5] gives 3 items (indices 2, 3, 4), not 4
• Use sequence[:] to make a shallow copy of a list, a common and idiomatic pattern
• Use [::-1] for a quick, readable way to reverse a string, list, or tuple
• Slicing never raises an IndexError even with out-of-range indices - it just returns as much as is available, unlike direct indexing

At a glance

Purpose

Scripting and general-purpose applications

File extension

.py

Runs in

Python interpreter

Usually used with

Python standard library and packages

Specifications & further reading

• Python language reference

Related Python documentation