pytest-dev/pytest · error · ValueError

{name}

Error message

{name}

What it means

Raised by CallSpec.getparam when the requested fixture/parameter name is not present in the CallSpec's params mapping. The exception message is just the missing name (a ValueError). This is an internal API used by pytest's fixture machinery to resolve a parameter value for a given argname within a specific callspec.

Source

Thrown at src/_pytest/python.py:1212

                raise nodes.Collector.CollectError(
                    f"{nodeid}: duplicate parametrization of {arg!r}"
                )
            params[arg] = val
            indices[arg] = param_index
            arg2scope[arg] = scope
        return CallSpec(
            params=params,
            indices=indices,
            _arg2scope=arg2scope,
            _idlist=self._idlist if id is HIDDEN_PARAM else [*self._idlist, id],
            marks=[*self.marks, *normalize_mark_list(marks)],
        )

    def getparam(self, name: str) -> object:
        try:
            return self.params[name]
        except KeyError as e:
            raise ValueError(name) from e

    @property
    def id(self) -> str:
        return "-".join(self._idlist)


if TYPE_CHECKING:
    # Deprecated alias kept for type checkers; runtime access goes through __getattr__.
    CallSpec2 = CallSpec


def get_direct_param_fixture_func(request: FixtureRequest) -> Any:
    return request.param


class DirectParamFixtureDef(FixtureDef[FixtureValue]):
    """A custom FixtureDef for direct parametrization fixtures.

View on GitHub (pinned to 98b357f69e)

Solutions

1. Check 'name in callspec.params' before calling getparam.
2. Use callspec.params.get(name, default) instead of getparam when absence is possible.
3. Verify the argname spelling matches the parametrize declaration.

Example fix

// before
val = callspec.getparam("usrname")  # typo
// after
if "username" in callspec.params:
    val = callspec.getparam("username")
else:
    val = None

name = "username"
if name in callspec.params:
    val = callspec.getparam(name)
else:
    val = callspec.params.get(name)

try:
    val = callspec.getparam(name)
except ValueError:
    val = None

When it happens

Trigger: Calling callspec.getparam('some_name') where 'some_name' was not part of the parametrize call that produced this callspec, or where the param was provided indirectly and not stored in params.

Common situations: Plugin or fixture code that introspects CallSpec objects and asks for an argname that doesn't exist for the current test; indirect parametrization where the name was misregistered; typos in argname lookups.

Related errors

• Empty parameter set in '{func.__name__}' at line {lineno + 1
• pytest.param cannot add pytest.mark.usefixtures; see https:/
• Expected id to be a string or a `pytest.HIDDEN_PARAM` sentin
• Unrecognized runpytest option: {self._method}
• Unknown parametrize_long_str_id_strategy: {value!r}. Valid v

AI-assisted analysis of pytest-dev/pytest@98b357f69e (2026-08-04). Data as JSON: /data/errors/9b0393bb9627a95b.json. Report an issue: GitHub.