pypa/pip · error · InvalidVersion

post must be non-negative integer, got {value}

Error message

post must be non-negative integer, got {value}

What it means

Raised by `_validate_post(value)` when the `post` argument to `Version.from_parts`/`__replace__` is not `None` and not a non-negative `int`. The post-release number in PEP 440 (`1.0.post1`) is a single non-negative integer; floats, strings, lists, and negatives are rejected. The validator wraps the int into `('post', value)` internally.

Source

Thrown at src/pip/_vendor/packaging/version.py:305

    if value is None:
        return value
    if isinstance(value, tuple) and len(value) == 2:
        letter, number = value
        letter = normalize_pre(letter)
        if letter in {"a", "b", "rc"} and isinstance(number, int) and number >= 0:
            # type checkers can't infer the Literal type here on letter
            return (letter, number)  # type: ignore[return-value]
    msg = f"pre must be a tuple of ('a'|'b'|'rc', non-negative int), got {value}"
    raise InvalidVersion(msg)


def _validate_post(value: object, /) -> tuple[Literal["post"], int] | None:
    if value is None:
        return value
    if isinstance(value, int) and value >= 0:
        return ("post", value)
    msg = f"post must be non-negative integer, got {value}"
    raise InvalidVersion(msg)


def _validate_dev(value: object, /) -> tuple[Literal["dev"], int] | None:
    if value is None:
        return value
    if isinstance(value, int) and value >= 0:
        return ("dev", value)
    msg = f"dev must be non-negative integer, got {value}"
    raise InvalidVersion(msg)


def _validate_local(value: object, /) -> LocalType | None:
    if value is None:
        return value
    if isinstance(value, str) and _LOCAL_PATTERN.fullmatch(value):
        return _parse_local_version(value)
    msg = f"local must be a valid version string, got {value!r}"
    raise InvalidVersion(msg)

View on GitHub (pinned to d7d0d0a394)

Solutions

1. Pass a non-negative `int`: `post=1`.
2. Coerce with `int(value)` and assert `>= 0` first.
3. For string input, use `Version('1.0.post1')`.
4. Omit `post` (`None`) if there is no post-release segment.

Example fix

// before
Version.from_parts(release=(1, 0), post='1')  # str -> raises

// after
Version.from_parts(release=(1, 0), post=int('1'))
# or
Version('1.0.post1')

def is_valid_post(value: object) -> bool:
    return value is None or (isinstance(value, int) and not isinstance(value, bool) and value >= 0)

def is_non_negative_int_or_none(value: object) -> bool:
    return value is None or (isinstance(value, int) and not isinstance(value, bool) and value >= 0)

from pip._vendor.packaging.version import Version, InvalidVersion

try:
    v = Version.from_parts(release=release, post=post)
except InvalidVersion as e:
    if 'post' in str(e):
        post = int(post)
        v = Version.from_parts(release=release, post=post)
    raise

When it happens

Trigger: `Version.from_parts(release=(1,0), post='1')`, `post=-1`, `post=1.5`, `post=[1]`. Check is `isinstance(value, int) and value >= 0`.

Common situations: Passing the post number as a string from config; a negative value from a buggy default; a float from arithmetic.

Related errors

• epoch must be non-negative integer, got {epoch}
• release must be a non-empty tuple of non-negative integers,
• pre must be a tuple of ('a'|'b'|'rc', non-negative int), got
• dev must be non-negative integer, got {value}
• local must be a valid version string, got {value!r}

AI-assisted analysis of pypa/pip@d7d0d0a394 (2026-08-04). Data as JSON: /data/errors/efd9347ba1d420e6.json. Report an issue: GitHub.