Type hints in namedtuple

Question

Consider following piece of code:

from collections import namedtuple
point = namedtuple("Point", ("x:int", "y:int"))

The Code above is just a way to demonstrate as to what I am trying to achieve.
I would like to make namedtuple with type hints.

Do you know any elegant way how to achieve result as intended?

Asked By: Pavel Hanpari

||

Source

Answer 1

You can use typing.NamedTuple

From the docs

Typed version of namedtuple.

>>> import typing
>>> Point = typing.NamedTuple("Point", [('x', int), ('y', int)])

This is present only in Python 3.5 onwards

Answered By: Bhargav Rao

Answer 2

The prefered Syntax for a typed named tuple since 3.6 is

from typing import NamedTuple

class Point(NamedTuple):
    x: int
    y: int = 1  # Set default value

Point(3)  # -> Point(x=3, y=1)

Edit
Starting Python 3.7, consider using dataclasses (your IDE may not yet support them for static type checking):

from dataclasses import dataclass

@dataclass
class Point:
    x: int
    y: int = 1  # Set default value

Point(3)  # -> Point(x=3, y=1)

Answered By: Wolfgang Kuehn

Answer 3

Just to be fair, NamedTuple from typing:

>>> from typing import NamedTuple
>>> class Point(NamedTuple):
...     x: int
...     y: int = 1  # Set default value
...
>>> Point(3)
Point(x=3, y=1)

equals to classic namedtuple:

>>> from collections import namedtuple
>>> p = namedtuple('Point', 'x,y', defaults=(1, ))
>>> p.__annotations__ = {'x': int, 'y': int}
>>> p(3)
Point(x=3, y=1)

So, NamedTuple is just syntax sugar for namedtuple

Below, you can find a creating NamedTuple function from the source code of python 3.10. As we can see, it uses collections.namedtuple constructor and adds __annotations__ from extracted types:

def _make_nmtuple(name, types, module, defaults = ()):
    fields = [n for n, t in types]
    types = {n: _type_check(t, f"field {n} annotation must be a type")
             for n, t in types}
    nm_tpl = collections.namedtuple(name, fields,
                                    defaults=defaults, module=module)
    nm_tpl.__annotations__ = nm_tpl.__new__.__annotations__ = types
    return nm_tpl

Answered By: mrvol

Type hints in namedtuple

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