3.2. Type Annotation Sequence

3.2.1. Rationale

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

  • 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]
>>> x  
>>> # 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]
>>> x  
>>> # IDE knows exactly what type is species
>>> # and what methods hint for autocompletion

3.2.2. Tuple

Generic type annotation:

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

Strict type annotation:

>>> 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')

3.2.3. List

Generic type annotation:

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

Strict type annotation:

>>> 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']

3.2.4. Set

Generic type annotation:

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

Strict type annotation:

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

3.2.5. Frozenset

Generic type annotation:

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

Strict type annotation:

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

3.2.6. 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:

>>> 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')]

3.2.7. List of Lists

Generic type annotation:

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

Strict type annotation:

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

3.2.8. Aliases

Generic type annotation:

>>> 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')]

3.2.9. Unions

Generic type annotation:

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

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

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

3.2.10. NamedTuple

>>> from typing import NamedTuple
>>> from sys import getsizeof
>>>
>>>
>>> class Astronaut(NamedTuple):
...     firstname: str
...     lastname: str
>>>
>>>
>>> astro = Astronaut('Mark', 'Watney')
>>> astro
Astronaut(firstname='Mark', lastname='Watney')
>>>
>>> getsizeof(astro)
56
>>>

>>> astro = ('Mark', 'Watney')
>>> getsizeof(astro)
56

3.2.11. 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')

>>> 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']

>>> 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'}

>>> 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'}

>>> from typing import List, Tuple
>>>
>>>
>>> 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')]
>>>
>>> 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')]

>>> from typing import List
>>>
>>>
>>> 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]]

>>> from typing import List, Tuple
>>>
>>>
>>> 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')]

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

3.2.12. Further Reading