Sequence operations¶

This reference covers operations common to all sequence types in Python: lists, tuples, strings, and ranges.

Common operations¶

Operation	Syntax	Lists	Tuples	Strings	Ranges
Indexing	`seq[i]`	Yes	Yes	Yes	Yes
Slicing	`seq[start:stop:step]`	Yes	Yes	Yes	Yes
Concatenation	`seq1 + seq2`	Yes	Yes	Yes	No
Repetition	`seq * n`	Yes	Yes	Yes	No
Membership	`item in seq`	Yes	Yes	Yes	Yes
Length	`len(seq)`	Yes	Yes	Yes	Yes
Minimum	`min(seq)`	Yes	Yes	Yes	Yes
Maximum	`max(seq)`	Yes	Yes	Yes	Yes
Index	`seq.index(value)`	Yes	Yes	Yes	Yes
Count	`seq.count(value)`	Yes	Yes	Yes	No

Indexing¶

Access a single item by its position. Python uses zero-based indexing.

colours = ["red", "green", "blue"]
print(colours[0])    # "red" (first item)
print(colours[-1])   # "blue" (last item)

Negative indices count from the end: -1 is the last item, -2 is the second to last, and so on.

Slicing¶

Extract a portion of a sequence using [start:stop:step].

Basic slicing¶

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

numbers[2:5]    # [2, 3, 4]
numbers[:3]     # [0, 1, 2]
numbers[7:]     # [7, 8, 9]
numbers[-3:]    # [7, 8, 9]

Slicing with step¶

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

Reversing¶

numbers[::-1]    # [9, 8, 7, 6, 5, 4, 3, 2, 1, 0]

Slice objects¶

You can create reusable slice objects:

first_three = slice(0, 3)
print(numbers[first_three])  # [0, 1, 2]

Unpacking¶

Basic unpacking¶

Assign each item to a separate variable:

x, y, z = [1, 2, 3]

The number of variables must match the number of items.

Extended unpacking with `*`¶

Use * to collect remaining items into a list:

first, *rest = [1, 2, 3, 4, 5]
# first = 1, rest = [2, 3, 4, 5]

first, *middle, last = [1, 2, 3, 4, 5]
# first = 1, middle = [2, 3, 4], last = 5

Nested unpacking¶

Unpack nested structures in a single statement:

(a, b), (c, d) = [1, 2], [3, 4]

Swapping values¶

a, b = b, a

Ignoring values¶

Use _ as a convention for values you do not need:

_, second, _ = (1, 2, 3)
first, *_ = [1, 2, 3, 4, 5]

Concatenation¶

Join two sequences of the same type:

[1, 2] + [3, 4]          # [1, 2, 3, 4]
(1, 2) + (3, 4)          # (1, 2, 3, 4)
"hello " + "world"       # "hello world"

Repetition¶

Repeat a sequence a given number of times:

[0] * 5          # [0, 0, 0, 0, 0]
(1, 2) * 3       # (1, 2, 1, 2, 1, 2)
"ha" * 3         # "hahaha"

Membership testing¶

Check whether an item exists in a sequence:

print(3 in [1, 2, 3])        # True
print("x" not in "hello")    # True

Comparison¶

Sequences of the same type can be compared. Comparison proceeds element by element:

[1, 2, 3] < [1, 2, 4]     # True
(1, 2) < (1, 2, 0)        # True
"apple" < "banana"        # True