3.9. Sequence Type Annotation

3.9.1. Rationale

  • Before Python 3.9 you need from typing import List, Set, Tuple, Dict

  • Since Python 3.9 - PEP 585 -- Type Hinting Generics In Standard Collections

>>> DATA = [(5.8, 2.7, 5.1, 1.9, 'virginica'),
...         (5.1, 3.5, 1.4, 0.2, 'setosa'),
...         (5.7, 2.8, 4.1, 1.3, 'versicolor')]
...
>>> x = DATA[0][-1]
... # IDE don't know what type is species
... # and cannot give hints for autocompletion

>>> DATA = [(5.8, 2.7, 5.1, 1.9, 'virginica'),
...         (5.1, 3.5, 1.4, 0.2, 'setosa'),
...         (5.7, 2.8, 4.1, 1.3, 'versicolor')]
...
>>> x: str = DATA[0][-1]
... # IDE knows exactly what type is species
... # and what methods hint for autocompletion

3.9.2. Tuple

Generic type annotation:

>>> data: tuple = ()
>>> data: tuple = tuple()
>>> data: tuple = 'a', 2, 3.3
>>> data: tuple = ('a', 2, 3.3)

Strict type annotation, since Python 3.9:

>>> data: tuple[int, int, int] = (1, 2, 3)
>>> data: tuple[str, str, str] = ('setosa', 'virginica', 'versicolor')
>>> data: tuple[str, int, float] = ('a', 2, 3.3)
>>> data: tuple[int, ...] = (1, 2, 3)
>>> data: tuple[str, ...] = ('setosa', 'virginica', 'versicolor')

Strict type annotation, before Python 3.9:

>>> from typing import Tuple
>>>
>>> data: Tuple[int, int, int] = (1, 2, 3)
>>> data: Tuple[str, str, str] = ('setosa', 'virginica', 'versicolor')
>>> data: Tuple[str, int, float] = ('a', 2, 3.3)
>>> data: Tuple[int, ...] = (1, 2, 3)
>>> data: Tuple[str, ...] = ('setosa', 'virginica', 'versicolor')

3.9.3. List

Generic type annotation:

>>> data: list = list()
>>> data: list = []
>>> data: list = ['a', 1, 2.2]

Strict type annotation, since Python 3.9:

>>> data: list[int] = [1, 2, 3, 4]
>>> data: list[float] = [5.8, 2.7, 5.1, 1.9]
>>> data: list[str] = ['a', 'b', 'c', 'd']

Strict type annotation, before Python 3.9:

>>> from typing import List
>>>
>>> data: List[int] = [1, 2, 3, 4]
>>> data: List[float] = [5.8, 2.7, 5.1, 1.9]
>>> data: List[str] = ['a', 'b', 'c', 'd']

3.9.4. Set

Generic type annotation:

>>> data: set = set()
>>> data: set = {'a', 1, 2.2}

Strict type annotation, since Python 3.9:

>>> data: set[int] = {1, 2, 3}
>>> data: set[float] = {0.0, 1.1, 2.2}
>>> data: set[str] = {'a', 'b', 'c'}

Strict type annotation, before Python 3.9:

>>> from typing import Set
>>>
>>> data: Set[int] = {1, 2, 3}
>>> data: Set[float] = {0.0, 1.1, 2.2}
>>> data: Set[str] = {'a', 'b', 'c'}

3.9.5. Frozenset

Generic type annotation:

>>> data: frozenset = set()
>>> data: frozenset = {'a', 1, 2.2}

Strict type annotation, since Python 3.9:

>>> data: frozenset[int] = {1, 2, 3}
>>> data: frozenset[float] = {0.0, 1.1, 2.2}
>>> data: frozenset[str] = {'a', 'b', 'c'}

Strict type annotation, before Python 3.9:

>>> from typing import FrozenSet
>>>
>>> data: FrozenSet[int] = {1, 2, 3}
>>> data: FrozenSet[float] = {0.0, 1.1, 2.2}
>>> data: FrozenSet[str] = {'a', 'b', 'c'}

3.9.6. List of Tuples

Generic type annotation:

>>> data: list[tuple] = [
...    (4.7, 3.2, 1.3, 0.2, 'setosa'),
...    (7.0, 3.2, 4.7, 1.4, 'versicolor'),
...    (7.6, 3.0, 6.6, 2.1, 'virginica')]

Strict type annotation, since Python 3.9:

>>> data: list[tuple[float, float, float, float, str]] = [
...    (4.7, 3.2, 1.3, 0.2, 'setosa'),
...    (7.0, 3.2, 4.7, 1.4, 'versicolor'),
...    (7.6, 3.0, 6.6, 2.1, 'virginica')]

Generic type annotation, before Python 3.9:

>>> from typing import List
>>>
>>> data: List[tuple] = [
...    (4.7, 3.2, 1.3, 0.2, 'setosa'),
...    (7.0, 3.2, 4.7, 1.4, 'versicolor'),
...    (7.6, 3.0, 6.6, 2.1, 'virginica')]

Strict type annotation, before Python 3.9:

>>> from typing import List, Tuple
>>>
>>> data: List[Tuple[float, float, float, float, str]] = [
...    (4.7, 3.2, 1.3, 0.2, 'setosa'),
...    (7.0, 3.2, 4.7, 1.4, 'versicolor'),
...    (7.6, 3.0, 6.6, 2.1, 'virginica')]

3.9.7. List of Lists

Generic type annotation:

>>> data: list[list] = [
...    [1, 2, 3],
...    [4, 5, 6],
...    [7, 8, 9]]

>>> data: list[list[int]] = [
...    [1, 2, 3],
...    [4, 5, 6],
...    [7, 8, 9]]

Generic type annotation, before Python 3.9:

>>> from typing import List
>>>
>>> data: List[list] = [
...    [1, 2, 3],
...    [4, 5, 6],
...    [7, 8, 9]]

Strict type annotation, since Python 3.9:

>>> from typing import List
>>>
>>> data: List[List[int]] = [
...    [1, 2, 3],
...    [4, 5, 6],
...    [7, 8, 9]]

3.9.8. Aliases

Generic type annotation:

>>> Point = tuple[int, int]
>>> locations: list[Point] = [
...    (0, 1),
...    (5, -3),
...    (-10, 20)]

>>> GeographicCoordinate = tuple[float, float]
>>> locations: list[GeographicCoordinate] = [
...    (25.91375, -60.15503),
...    (-11.01983, -166.48477),
...    (-11.01983, -166.48477)]

>>> Iris = tuple[float, float, float, float, str]
>>> data: list[Iris] = [
...    (4.7, 3.2, 1.3, 0.2, 'setosa'),
...    (7.0, 3.2, 4.7, 1.4, 'versicolor'),
...    (7.6, 3.0, 6.6, 2.1, 'virginica')]

Strict type annotation, before Python 3.9:

>>> GeographicCoordinate = Tuple[float, float]
>>> locations: List[GeographicCoordinate] = [
...    (25.91375, -60.15503),
...    (-11.01983, -166.48477),
...    (-11.01983, -166.48477)]

>>> Iris = Tuple[float, float, float, float, str]
>>> data: List[Iris] = [
...    (4.7, 3.2, 1.3, 0.2, 'setosa'),
...    (7.0, 3.2, 4.7, 1.4, 'versicolor'),
...    (7.6, 3.0, 6.6, 2.1, 'virginica')]

3.9.9. Unions

Generic type annotation:

>>> from typing import Union
>>>
>>> data: list[Union[list, tuple, set]] = [
...    [1, 2, 3],
...    (4, 5, 6),
...    {7, 8, 9}]

>>> from typing import Union
>>>
>>> data: list[Union[list[int], tuple[int, ...], set[int]]] = [
...    [1, 2, 3],
...    (4, 5, 6),
...    {7, 8, 9}]

>>> from typing import Union
>>>
>>> row = Union[list[int], tuple[int, ...], set[int]]
>>> data: list[row] = [
...    [1, 2, 3],
...    (4, 5, 6),
...    {7, 8, 9}]

Strict type annotation, before Python 3.9:

>>> from typing import Union, List
>>>
>>> data: List[Union[list, tuple, set]] = [
...    [1, 2, 3],
...    (4, 5, 6),
...    {7, 8, 9}]

>>> from typing import Union, List, Tuple, Set
>>>
>>> data: List[Union[List[int], Tuple[int, int, int], Set[int]]] = [
...    [1, 2, 3],
...    (4, 5, 6),
...    {7, 8, 9}]

>>> from typing import Union, List, Tuple, Set
>>>
>>> Row = Union[List[int],
...             Tuple[int, int, int],
...             Set[int]]
...
>>> data: List[Row] = [
...    [1, 2, 3],
...    (4, 5, 6),
...    {7, 8, 9}]

3.9.10. Further Reading