replace-namedtuple-class.md

replace-namedtuple-class

The typing.NamedTuple class is often easier to create than a @dataclass. The difference is that a namedtuple is not mutable. You can change fields only by using the ._replace() method on the object creating a new object.

A function variant of namedtuple did exist in collections since python 2.6. The transformer will look for the fields in the NamedTuple class definition and generate a function variant out of it.

Naturally, the namedtuple function can NOT be extended with helper methods like the class-based NamedTuple can. The transformer will raise an Exception when it finds a local def in a NamedTuple class - so you are restricted in writing code that can be run on older python versions with this transformer.

Nethertheless, using simple NamedTuple-based classes is much easier to read than the function-based namedtuple, AND type checkers can help tracking the correct type for the fields of each instance.

    # original
    from typing import NamedTuple
    import socket

    class A(NamedTuple):
        b: int
        c: socket.socket

    # transformed
    from collections import namedtuple
    import socket
    A = namedtuple('A', ['b', 'c'])