How to alias class attributes when creating NamedTuple?

Question

I want to alias project_version with init_version, but since NamedTuple is a factory method I'm having difficulty in doing this.

from typing import NamedTuple

class ProjectMetadata(NamedTuple):
    """Structure holding project metadata derived from `pyproject.toml`"""

    config_file: Path
    package_name: str
    project_name: str
    project_path: Path
    project_version: str
    source_dir: Path

I've tried the basic alias technique but met with undefined init_version errors.

from typing import NamedTuple

class ProjectMetadata(NamedTuple):
    """Structure holding project metadata derived from `pyproject.toml`"""

    config_file: Path
    package_name: str
    project_name: str
    project_path: Path
    project_version: str = init_version
    source_dir: Path

Have you considered using a dataclass instead? Then set frozen=True to prevent assignment. See Is there an alias or name parameter for dataclass arguments? — Gino Mempin
– Gino Mempin, Commented Jan 24, 2023 at 13:44
What exactly do you mean by "alias"? Do you want that you can access metadata.init_version and get metadata.project_version? — mkrieger1
– mkrieger1, Commented Jan 24, 2023 at 13:53
And if so, why do you think that's preferable to having a single name for this particular attribute of your data structure? — chepner
– chepner, Commented Jan 24, 2023 at 13:54
This is part of a much larger codebase, essentially I want to deprecate project_version by renaming it with init_version but still want it to be backwards compatible. I can't change it directly as this would be a breaking change and not backwards compatible. I want to treat project_version and init_version as being the same. — Blueynuey
– Blueynuey, Commented Jan 24, 2023 at 14:41

mkrieger1 · Accepted Answer · 2023-01-24 14:50:58Z

2

You can simply add a property named init_version to the class which returns the project_version attribute:

class ProjectMetadata(NamedTuple):
    # ...
    project_version: str

    @property
    def init_version(self) -> str:
        return self.project_version

answered Jan 24, 2023 at 14:50

mkrieger1

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