Lists and Tuples

Lists — ordered, mutable sequences

A list is Python’s workhorse container. It holds an ordered sequence of any objects and supports in-place mutation.

fruits = ['apple', 'banana', 'cherry']
fruits.append('date')        # add to end
fruits.insert(1, 'avocado')  # insert before index 1
fruits.remove('banana')      # remove first occurrence
print(fruits)                # ['apple', 'avocado', 'cherry', 'date']

Common list methods

Method	Description
`append(x)`	Add `x` to the end
`insert(i, x)`	Insert `x` before index `i`
`remove(x)`	Remove first occurrence of `x`
`pop(i=-1)`	Remove and return item at index `i`
`sort(key=None, reverse=False)`	Sort in place
`reverse()`	Reverse in place
`index(x)`	Return index of first occurrence of `x`
`count(x)`	Count occurrences of `x`

Sorting

list.sort() sorts in place and returns None. Pass a key function to sort by an arbitrary criterion.

numbers = [5, 2, 8, 1, 9, 3]
numbers.sort()
print(numbers)  # [1, 2, 3, 5, 8, 9]

words = ['banana', 'apple', 'cherry']
words.sort(key=len)
print(words)    # ['apple', 'banana', 'cherry']

Use sorted(iterable) instead of .sort() when you need a new list and want to leave the original unchanged.

Tuples — ordered, immutable sequences

A tuple is like a list but cannot be modified after creation. Use tuples to represent fixed records where position carries meaning.

rgb = (255, 128, 0)   # an orange colour
point = (3.0, 4.0)    # a 2-D coordinate
row = (1, 'Alice', 42)  # a database row

Tuple unpacking

Python lets you unpack a tuple (or any iterable) directly into variables. The number of variables must match the length — unless you use * to capture the rest.

coords = (10.5, 20.3, 30.1)
x, y, z = coords
print(x, y, z)           # 10.5 20.3 30.1

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

Accessing tuple fields by index

Without a name, tuple fields are accessed by integer index. Assign constants for readability:

RGB = (255, 128, 0)
RED   = 0
GREEN = 1
BLUE  = 2

print(RGB[RED])    # 255
print(RGB[GREEN])  # 128
print(RGB[BLUE])   # 0

For a more ergonomic approach, use collections.namedtuple or typing.NamedTuple.

Full runnable demo

Open in an online REPL

# --- list mutation and sorting ---
fruits = ['apple', 'banana', 'cherry']
fruits.append('date')
fruits.insert(1, 'avocado')
print('after insert:', fruits)

fruits.remove('banana')
print('after remove:', fruits)

numbers = [5, 2, 8, 1, 9, 3]
numbers.sort()
print('sorted:', numbers)

words = ['banana', 'apple', 'cherry']
words.sort(key=len)
print('by length:', words)

# --- tuple unpacking ---
coords = (10.5, 20.3, 30.1)
x, y, z = coords
print('unpacked:', x, y, z)

first, *rest = [1, 2, 3, 4, 5]
print('first:', first)
print('rest:', rest)

# --- named fields via index constants ---
RGB = (255, 128, 0)
print('red:', RGB[0], 'green:', RGB[1], 'blue:', RGB[2])