def render_pep440_old(pieces: Dict[str, Any]) -> str:
    """TAG[.postDISTANCE[.dev0]] .

    The ".dev0" means dirty.

    Exceptions:
    1: no tags. 0.postDISTANCE[.dev0]
    """
    if pieces["closest-tag"]:
        rendered = pieces["closest-tag"]
        if pieces["distance"] or pieces["dirty"]:
            rendered += ".post%d" % pieces["distance"]
            if pieces["dirty"]:
                rendered += ".dev0"
    else:
        # exception #1
        rendered = "0.post%d" % pieces["distance"]
        if pieces["dirty"]:
            rendered += ".dev0"
    return rendered
TAG[.postDISTANCE[.dev0]] .

The ".dev0" means dirty.

Exceptions:
1: no tags. 0.postDISTANCE[.dev0]
s3fs/_version.py