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Add variance checks to aggregation tests and type assertions #1546

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42e67a5
Add variance checks to aggregation tests and type assertions
roman-y-wu Dec 13, 2025
adb98a5
Undo the tests/_typing.py change
roman-y-wu Dec 13, 2025
48b7070
TYP: Fix Series.var() return type annotations:
roman-y-wu Dec 16, 2025
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32 changes: 30 additions & 2 deletions pandas-stubs/core/series.pyi
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Original file line number Diff line number Diff line change
Expand Up @@ -4610,14 +4610,42 @@ class Series(IndexOpsMixin[S1], ElementOpsMixin[S1], NDFrame):
**kwargs: Any,
) -> np_1darray: ...
def tolist(self) -> list[S1]: ...
@overload
def var(
self,
self: Series[Never],
axis: AxisIndex | None = 0,
skipna: _bool | None = True,
ddof: int = 1,
numeric_only: _bool = False,
**kwargs: Any,
) -> Scalar: ...
) -> float: ...
@overload
def var(
self: Series[Timedelta],
axis: AxisIndex | None = 0,
skipna: _bool | None = True,
ddof: int = 1,
numeric_only: _bool = False,
**kwargs: Any,
) -> Never: ...
@overload
def var(
self: Series[complex],
axis: AxisIndex | None = 0,
skipna: _bool | None = True,
ddof: int = 1,
numeric_only: _bool = False,
**kwargs: Any,
) -> float: ...
@overload
def var(
self: SupportsGetItem[Scalar, SupportsTruedivInt[S2]],
axis: AxisIndex | None = 0,
skipna: _bool | None = True,
ddof: int = 1,
numeric_only: _bool = False,
**kwargs: Any,
) -> S2: ...
# Rename axis with `mapper`, `axis`, and `inplace=True`
@overload
def rename_axis(
Expand Down
13 changes: 13 additions & 0 deletions tests/series/test_agg.py
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Original file line number Diff line number Diff line change
Expand Up @@ -14,27 +14,31 @@ def test_agg_any_float() -> None:
check(assert_type(series.mean(), float), np.float64)
check(assert_type(series.median(), float), np.float64)
check(assert_type(series.std(), float), np.float64)
check(assert_type(series.var(), float), np.float64)


def test_agg_bool() -> None:
series = pd.Series([True, False, True])
check(assert_type(series.mean(), float), np.float64)
check(assert_type(series.median(), float), np.float64)
check(assert_type(series.std(), float), np.float64)
check(assert_type(series.var(), float), np.float64)


def test_agg_int() -> None:
series = pd.Series([3, 1, 2])
check(assert_type(series.mean(), float), np.float64)
check(assert_type(series.median(), float), np.float64)
check(assert_type(series.std(), float), np.float64)
check(assert_type(series.var(), float), np.float64)


def test_agg_float() -> None:
series = pd.Series([3.0, float("nan"), 2.0])
check(assert_type(series.mean(), float), np.float64)
check(assert_type(series.median(), float), np.float64)
check(assert_type(series.std(), float), np.float64)
check(assert_type(series.var(), float), np.float64)


def test_agg_complex() -> None:
Expand All @@ -57,6 +61,12 @@ def test_agg_complex() -> None:
),
):
check(assert_type(series.std(), np.float64), np.float64)
with pytest_warns_bounded(
np.exceptions.ComplexWarning,
r"Casting complex values to real discards the imaginary part",
upper="2.3.99",
):
check(assert_type(series.var(), float), np.float64)


def test_agg_str() -> None:
Expand All @@ -65,6 +75,7 @@ def test_agg_str() -> None:
series.mean() # type: ignore[misc] # pyright: ignore[reportAttributeAccessIssue]
series.median() # type: ignore[misc] # pyright: ignore[reportAttributeAccessIssue]
series.std() # type: ignore[misc] # pyright: ignore[reportAttributeAccessIssue]
series.var() # type: ignore[misc] # pyright: ignore[reportAttributeAccessIssue]


def test_agg_ts() -> None:
Expand All @@ -83,3 +94,5 @@ def test_agg_td() -> None:
check(assert_type(series.mean(), pd.Timedelta), pd.Timedelta)
check(assert_type(series.median(), pd.Timedelta), pd.Timedelta)
check(assert_type(series.std(), pd.Timedelta), pd.Timedelta)
if TYPE_CHECKING_INVALID_USAGE:
series.var() # type: ignore[misc]
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@cmp0xff cmp0xff Dec 16, 2025

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Never is considered as "valid" by type checkers. However if a function call returns Never, type checkers won't check the code after that call.

You can do something like this:

Suggested change
series.var() # type: ignore[misc]
def _0() -> None: # pyright: ignore[reportUnusedFunction]
assert_type(series.var(), Never)

6 changes: 3 additions & 3 deletions tests/series/test_series.py
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Original file line number Diff line number Diff line change
Expand Up @@ -780,9 +780,9 @@ def test_types_abs() -> None:

def test_types_var() -> None:
s = pd.Series([-10, 2, 3, 10])
s.var()
s.var(axis=0, ddof=1)
s.var(skipna=True, numeric_only=False)
check(assert_type(s.var(), float), np.float64)
check(assert_type(s.var(axis=0, ddof=1), float), np.float64)
check(assert_type(s.var(skipna=True, numeric_only=False), float), np.float64)


def test_types_std() -> None:
Expand Down
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