5.5. Type Annotation Sequences

  • 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

5.5.1. 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]]

5.5.2. 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')]

5.5.3. 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'}]

5.5.4. 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'}]

5.5.5. 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'))

5.5.6. Use Case - 0x01

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

5.5.7. 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}]

5.5.8. Further Reading

5.5.9. References

1

https://docs.python.org/3/library/typing.html#module-contents