pypa/pip · error · InstallationError

Error parsing

Error message

Error parsing {path}: {e}

What it means

The pyproject.toml file exists but contains invalid TOML syntax. The _load_pyproject helper caught a tomllib.TOMLDecodeError (e.g. duplicate keys, unclosed brackets, invalid escape sequences) and wrapped it in an InstallationError.

Solutions

1. Validate the TOML: 'python -c "import tomllib; tomllib.load(open('pyproject.toml','rb'))"' to get a line-number error
2. Check for merge-conflict markers and remove them
3. Look for duplicate keys or table headers
4. Use a TOML linter or IDE with TOML validation

from pip._internal.utils.compat import tomllib

def validate_pyproject_toml(path: str) -> bool:
    try:
        with open(path, "rb") as fp:
            tomllib.load(fp)
        return True
    except tomllib.TOMLDecodeError:
        return False

if not validate_pyproject_toml("pyproject.toml"):
    print("pyproject.toml has TOML syntax errors")

from pip._internal.utils.compat import tomllib

def is_valid_toml_file(path: str) -> bool:
    """Type guard: True if the file parses as valid TOML."""
    try:
        with open(path, "rb") as fp:
            tomllib.load(fp)
        return True
    except (tomllib.TOMLDecodeError, OSError):
        return False

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 "Error parsing" in str(e):
        print("Fix TOML syntax in pyproject.toml")
    else:
        raise

When it happens

Trigger: pyproject.toml has a syntax error such as a duplicate table header, an unterminated string, or an invalid value. tomllib.load() raises TOMLDecodeError.

Common situations: Hand-editing pyproject.toml and introducing a typo. Merge conflicts leaving conflict markers (<<<<<<<) in the file. Tooling that generates malformed TOML. Missing quotes around values.

Related errors

• [dependency-groups] resolution failed for
• [dependency-groups] table was malformed in
• [dependency-groups] table was missing from
• Error reading
• Failed to parse TOML in

AI-assisted analysis of pypa/pip@f399c37189 (2026-08-08). Data as JSON: /api/errors/54109bd34aeab893. Report an issue: GitHub.

Appendix: source

Thrown at src/pip/_internal/req/req_dependency_group.py:84

                f"[dependency-groups] data was invalid in {path}: {'; '.join(messages)}"
            ) from eg

    return resolvers


def _load_pyproject(path: str) -> dict[str, Any]:
    """
    This helper loads a pyproject.toml as TOML.

    It raises an InstallationError if the operation fails.
    """
    try:
        with open(path, "rb") as fp:
            return tomllib.load(fp)
    except FileNotFoundError:
        raise InstallationError(f"{path} not found. Cannot resolve '--group' option.")
    except tomllib.TOMLDecodeError as e:
        raise InstallationError(f"Error parsing {path}: {e}") from e
    except OSError as e:
        raise InstallationError(f"Error reading {path}: {e}") from e

View on GitHub (pinned to f399c37189)