3.5. Type Annotation Sequences
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
3.5.1. List of Lists
Declaration:
>>> data: list
>>> data: list[list]
>>> data: list[list[int]]
Example:
>>> data: list = [
... [1, 2, 3],
... [4, 5, 6],
... [7, 8, 9]]
>>> 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]]
3.5.2. List of Tuples
Declaration:
>>> data: list
>>> data: list[tuple]
>>> data: list[tuple[float, float, float, float, str]]
Example:
>>> 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')]
>>> 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')]
3.5.3. List of Dicts
>>> data: list[dict] = [
... {'features': [4.7, 3.2, 1.3, 0.2], 'label': 'setosa'},
... {'features': [7.0, 3.2, 4.7, 1.4], 'label': 'versicolor'},
... {'features': [7.6, 3.0, 6.6, 2.1], 'label': 'virginica'}]
>>> data: list[dict[str, list[float] | str]] = [
... {'features': [4.7, 3.2, 1.3, 0.2], 'label': 'setosa'},
... {'features': [7.0, 3.2, 4.7, 1.4], 'label': 'versicolor'},
... {'features': [7.6, 3.0, 6.6, 2.1], 'label': 'virginica'}]
3.5.4. Aliases
Declaration:
>>> row = tuple[int, int, int]
>>> data: list[row]
Example:
>>> 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')]
>>> features = list[float]
>>> label = str
>>>
>>> data: list[dict[str, features|label]] = [
... {'features': [4.7, 3.2, 1.3, 0.2], 'label': 'setosa'},
... {'features': [7.0, 3.2, 4.7, 1.4], 'label': 'versicolor'},
... {'features': [7.6, 3.0, 6.6, 2.1], 'label': 'virginica'}]
3.5.5. Unions
Declaration:
>>> a = tuple[str, str, str]
>>> b = tuple[int, int, int]
>>> c = tuple[float, float, float]
>>>
>>> data: list[a | b | c]
>>> header = tuple[str, str, str]
>>> row = tuple[int, int, int]
>>>
>>> data: tuple[header,row,...]
Example:
>>> 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'))
3.5.6. Use Case - 0x01
>>> GeographicCoordinate = tuple[float, float]
>>>
>>> locations: list[GeographicCoordinate] = [
... (25.91375, -60.15503),
... (-11.01983, -166.48477),
... (-11.01983, -166.48477)]
3.5.7. Use Case - 0x02
>>> 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}]
3.5.8. Further Reading
More information in Type Annotations
More information in CI/CD Type Checking