pypa/pip · error · InstallationError

[dependency-groups] resolution failed for '{groupname}' from

Error message

[dependency-groups] resolution failed for '{groupname}' from '{path}': {'; '.join(messages)}

What it means

Raised by _resolve_all_groups() when DependencyGroupResolver.resolve(groupname) raises an ExceptionGroup while resolving a specific `[dependency-groups]` entry (req_dependency_group.py:32-38). All sub-exception messages are joined into a single InstallationError. This means the group was found but one or more requirement specifiers inside it are invalid or reference other groups incorrectly.

Source

Thrown at src/pip/_internal/req/req_dependency_group.py:35

    resolvers = _build_resolvers(path for (path, _) in groups)
    return list(_resolve_all_groups(resolvers, groups))


def _resolve_all_groups(
    resolvers: dict[str, DependencyGroupResolver], groups: list[tuple[str, str]]
) -> Iterator[str]:
    """
    Run all resolution, converting any error from `DependencyGroupResolver` into
    an InstallationError.
    """
    for path, groupname in groups:
        resolver = resolvers[path]
        try:
            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"]

View on GitHub (pinned to d7d0d0a394)

Solutions

Read the joined messages in the error — each names a specific malformed entry; fix each one.
Ensure every requirement string in the group is valid PEP 508 (test with packaging.requirements.Requirement).
For group-to-group references using `{other}`, confirm the referenced group exists and is not circular.
Re-run `pip install --group mygroup` after corrections.

Example fix

# before
[dependency-groups]
mygroup = ["requests", "bad =spec"]
# after
[dependency-groups]
mygroup = ["requests", "otherpkg>=1.0"]

Defensive patterns

Strategy: validation

Validate before calling

import tomllib
from pip._vendor.packaging.dependency_groups import DependencyGroupResolver
from pip._vendor.packaging.errors import ExceptionGroup

def validate_group_resolves(path: str, group: str) -> list[str]:
    with open(path, "rb") as f:
        data = tomllib.load(f)
    raw = data.get("dependency-groups", {})
    resolver = DependencyGroupResolver(raw)
    try:
        return [str(r) for r in resolver.resolve(group)]
    except ExceptionGroup as eg:
        raise ValueError("; ".join(str(e) for e in eg.exceptions)) from eg

Type guard

null

Try / catch

from pip._internal.exceptions import InstallationError

try:
    parse_dependency_groups([(path, group)])
except InstallationError as e:
    if "resolution failed" in str(e):
        # show the joined sub-error messages to the user
        ...
    raise

Prevention

Validate every requirement string inside [dependency-groups] with packaging.requirements.Requirement in CI.
Avoid circular or undefined `{group}` references.
Test `pip install --group <name>` locally before pushing changes.

When it happens

Trigger: Using `pip install --group mygroup` where pyproject.toml's [dependency-groups] has a malformed entry, an invalid PEP 508 requirement, a circular group reference, or references a non-existent group. The resolver (from packaging.dependency_groups) bundles failures into an ExceptionGroup which pip flattens.

Common situations: Typos in requirement specifiers within a dependency group. Self-referential or mutually-referential groups. Referencing an undefined group via `{another-group}` syntax. Migrating requirements files into groups with transcription errors.

Related errors

AI-assisted analysis of pypa/pip@d7d0d0a394 (2026-08-04). Data as JSON: /data/errors/fd7d6b14e0d018cd.json. Report an issue: GitHub.