What causes "unknown configuration type: {type}" in pytest-dev/pytest?

Use one of the standard ini types ("string", "paths", "pathlist", "args", "linelist", "bool") in `addini`.

pytest-dev/pytest · error · ValueError

unknown configuration type: {type}

Error message

unknown configuration type: {type}

What it means

Raised by the legacy-path compatibility shim `Config__getini_unknown_type` when `config.getini(name)` encounters an ini option whose registered type is neither a standard pytest type nor the legacy "pathlist". The shim only knows how to convert "pathlist"; any other unknown type string bubbles up as ValueError carrying the type and value.

Source

Thrown at src/_pytest/legacypath.py:395

def Session_startdir(self: Session) -> LEGACY_PATH:
    """The path from which pytest was invoked.

    Prefer to use ``startpath`` which is a :class:`pathlib.Path`.

    :type: LEGACY_PATH
    """
    return legacy_path(self.startpath)


def Config__getini_unknown_type(self, name: str, type: str, value: str | list[str]):
    if type == "pathlist":
        # TODO: This assert is probably not valid in all cases.
        assert self.inipath is not None
        dp = self.inipath.parent
        input_values = shlex.split(value) if isinstance(value, str) else value
        return [legacy_path(str(dp / x)) for x in input_values]
    else:
        raise ValueError(f"unknown configuration type: {type}", value)


def Node_fspath(self: Node) -> LEGACY_PATH:
    """(deprecated) returns a legacy_path copy of self.path"""
    return legacy_path(self.path)


def Node_fspath_set(self: Node, value: LEGACY_PATH) -> None:
    self.path = Path(value)


@hookimpl(tryfirst=True)
def pytest_load_initial_conftests(early_config: Config) -> None:
    """Monkeypatch legacy path attributes in several classes, as early as possible."""
    mp = MonkeyPatch()
    early_config.add_cleanup(mp.undo)

    # Add Cache.makedir().

View on GitHub (pinned to 98b357f69e)

Solutions

Use one of the standard ini types ("string", "paths", "pathlist", "args", "linelist", "bool") in `addini`.
If a custom type is needed, handle parsing yourself and register the option as a plain string.
Update/check the plugin that registered the option for a typo or incompatible type name.

Example fix

// before
parser.addini("my_opt", type="json", default="{}")  # unknown type
// after
parser.addini("my_opt", type="string", default="{}")
# then parse JSON yourself when reading

Defensive patterns

Strategy: validation

Validate before calling

VALID_INI_TYPES = {"string", "paths", "pathlist", "args", "linelist", "bool"}

def safe_addini(parser, name, type=None, **kw):
    if type is not None and type not in VALID_INI_TYPES:
        raise ValueError(f"unknown configuration type: {type}")
    parser.addini(name, type=type, **kw)

Type guard

def is_known_ini_type(type_name: str) -> bool:
    return type_name in {"string", "paths", "pathlist", "args", "linelist", "bool"}

Prevention

Use only standard ini types when registering options.
Parse custom formats yourself from a string-typed option.
Check for typos in the type argument.

When it happens

Trigger: A plugin registers an ini option with a non-standard `type=` value (e.g. `type="json"`) and the value is later read through the legacy path layer, or `legacypath` is the only handler available for that type. The error reports the offending type string.

Common situations: Custom plugin defining a bespoke ini type. Version mismatch between a plugin and pytest where a type name changed. Mis-typed `addini(..., type="sting")` typo.

Related errors

AI-assisted analysis of pytest-dev/pytest@98b357f69e (2026-08-04). Data as JSON: /data/errors/858d32903583257a.json. Report an issue: GitHub.