07fk-typing-namedtuple.md

typing.NamedTuple

#python #programming #datastructure #data #storage #class

• They are immutable because of inheritance of tuple
• Class syntax
• Use inspect.get_annotations(myclass) to see about field need to be annotated
• Can use default values on fields

from typing import NamedTuple
class Coordinate(NamedTuple):
    lat: float
    lon: float
    reference: str = 'WGS84'

• How to inspect with NamedTuple:

import typing
class DemoNTClass(typing.NamedTuple):
    a: int
    b: float = 1.1
    c = 'spam'

>>> from demo_nt import DemoNTClass
>>> DemoNTClass.__annotations__
{'a': <class 'int'>, 'b': <class 'float'>}
>>> DemoNTClass.a
<_collections._tuplegetter object at 0x101f0f940>
>>> DemoNTClass.b
<_collections._tuplegetter object at 0x101f0f8b0>
>>> DemoNTClass.c
'spam'

• C in that case is a class attribute, and not a field (instance attribute)
• Parameter a is needed here
• b have default value, which is 1.1

References

• Ramalho, 2022, p172-179
• Ramalho, 2022, p183-187