3.2. Type Annotation Sequence¶
Before Python 3.9 you need
from typing import List, Tuple, Set, FrozensetSince 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
3.2.1. 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')
3.2.2. 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']
3.2.3. 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'}
3.2.4. 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'}
3.2.5. List of Tuples¶
Generic type annotation:
>>> data: list = [
... (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] = [
... (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')]
3.2.6. List of Lists¶
Generic type annotation:
>>> data: list = [
... [1, 2, 3],
... [4, 5, 6],
... [7, 8, 9]]
>>> 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]]
3.2.7. 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')]
3.2.8. 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}]
>>> Header = tuple[str, str, str, str, str]
>>> Row = tuple[float, float, float, float, str]
>>>
>>> DATA: tuple[Header|Row,...] = (
... ('Sepal length', 'Sepal width', 'Petal length', 'Petal width', 'Species'),
... (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'),
... (6.3, 2.9, 5.6, 1.8, 'virginica'),
... (6.4, 3.2, 4.5, 1.5, 'versicolor'),
... (4.7, 3.2, 1.3, 0.2, 'setosa'))
3.2.9. NamedTuple¶
>>> from typing import NamedTuple
>>> from sys import getsizeof
>>>
>>>
>>> class Astronaut(NamedTuple):
... firstname: str
... lastname: str
>>>
>>>
>>> mark = Astronaut('Mark', 'Watney')
>>> mark
Astronaut(firstname='Mark', lastname='Watney')
>>> a = ('Mark', 'Watney')
>>> b = Astronaut('Mark', 'Watney')
>>>
>>> a == b
True
>>>
>>> getsizeof(a)
56
>>> getsizeof(b)
56
3.2.10. Further Reading¶
More information in Type Annotations
More information in CI/CD Type Checking