pypa/pip · error · InstallationError

[dependency-groups] table was missing from

Error message

[dependency-groups] table was missing from '{path}'. Cannot resolve '--group' option.

What it means

pip was asked to resolve a '--group' but the specified pyproject.toml does not contain a '[dependency-groups]' table at all. Without this table, there are no groups to resolve, so pip aborts early in _build_resolvers().

Solutions

Add a [dependency-groups] table to your pyproject.toml with at least one group
Verify you are pointing at the correct pyproject.toml if using a custom path
Remove the --group flag if your project does not use dependency groups

Example fix

# before — pyproject.toml has no dependency-groups
[project]
name = "mypackage"

# after
[project]
name = "mypackage"

[dependency-groups]
dev = ["pytest", "ruff"]

Defensive patterns

Strategy: validation

Validate before calling

from pip._internal.utils.compat import tomllib

def has_dependency_groups_table(path: str) -> bool:
    with open(path, "rb") as fp:
        data = tomllib.load(fp)
    return "dependency-groups" in data

if not has_dependency_groups_table("pyproject.toml"):
    print("No [dependency-groups] table — add one or remove --group")

Type guard

from pip._internal.utils.compat import tomllib

def has_dependency_groups(path: str) -> bool:
    """Type guard: True if pyproject.toml has a [dependency-groups] table."""
    with open(path, "rb") as fp:
        return "dependency-groups" in tomllib.load(fp)

Try / catch

from pip._internal.exceptions import InstallationError
from pip._internal.req.req_dependency_group import parse_dependency_groups

try:
    reqs = parse_dependency_groups([("pyproject.toml", "dev")])
except InstallationError as e:
    if "table was missing" in str(e):
        print("Add a [dependency-groups] table to pyproject.toml")
    else:
        raise

Prevention

Add a [dependency-groups] table before using --group
Validate pyproject.toml has the table in CI before invoking pip --group
Remove the --group flag if your project does not use dependency groups

When it happens

Trigger: Running 'pip install --group dev' in a project whose pyproject.toml has no [dependency-groups] section. The check 'if dependency-groups not in pyproject' fails.

Common situations: Project has not adopted PEP 735 dependency groups yet. Wrong pyproject.toml path was specified. The table was accidentally removed or renamed during editing.

Related errors

AI-assisted analysis of pypa/pip@f399c37189 (2026-08-08). Data as JSON: /api/errors/2a20bd7614aee708. Report an issue: GitHub.

Appendix: source

Thrown at src/pip/_internal/req/req_dependency_group.py:49

            yield from (str(req) for req in resolver.resolve(groupname))
        except ExceptionGroup as eg:
            # Convert ExceptionGroup to a single InstallationError with all messages
            messages = [str(e) for e in eg.exceptions]
            raise InstallationError(
                f"[dependency-groups] resolution failed for '{groupname}' "
                f"from '{path}': {'; '.join(messages)}"
            ) from eg


def _build_resolvers(paths: Iterable[str]) -> dict[str, Any]:
    resolvers = {}
    for path in paths:
        if path in resolvers:
            continue

        pyproject = _load_pyproject(path)
        if "dependency-groups" not in pyproject:
            raise InstallationError(
                f"[dependency-groups] table was missing from '{path}'. "
                "Cannot resolve '--group' option."
            )
        raw_dependency_groups = pyproject["dependency-groups"]
        if not isinstance(raw_dependency_groups, dict):
            raise InstallationError(
                f"[dependency-groups] table was malformed in {path}. "
                "Cannot resolve '--group' option."
            )

        try:
            resolvers[path] = DependencyGroupResolver(raw_dependency_groups)
        except ExceptionGroup as eg:
            # Handle ExceptionGroup from resolver initialization
            messages = [str(e) for e in eg.exceptions]
            raise InstallationError(
                f"[dependency-groups] data was invalid in {path}: {'; '.join(messages)}"
            ) from eg

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