DEPR: Enforce expanding(center) deprecation

doc/source/whatsnew/v2.0.0.rst

@@ -147,6 +147,7 @@ Removal of prior version deprecations/changes
 - Disallow passing non-round floats to :class:`Timestamp` with ``unit="M"`` or ``unit="Y"`` (:issue:`47266`)
 - Removed :func:`is_extension_type` in favor of :func:`is_extension_array_dtype` (:issue:`29457`)
 - Remove :meth:`DataFrameGroupBy.pad` and :meth:`DataFrameGroupBy.backfill` (:issue:`45076`)
+- Removed the ``center`` keyword in :meth:`DataFrame.expanding` (:issue:`20647`)
 - Enforced :meth:`Rolling.count` with ``min_periods=None`` to default to the size of the window (:issue:`31302`)
 
 .. ---------------------------------------------------------------------------

pandas/core/generic.py

@@ -12095,23 +12095,11 @@ def rolling(
     def expanding(
         self,
         min_periods: int = 1,
-        center: bool_t | None = None,
         axis: Axis = 0,
         method: str = "single",
     ) -> Expanding:
         axis = self._get_axis_number(axis)
-        if center is not None:
-            warnings.warn(
-                "The `center` argument on `expanding` will be removed in the future.",
-                FutureWarning,
-                stacklevel=find_stack_level(),
-            )
-        else:
-            center = False
-
-        return Expanding(
-            self, min_periods=min_periods, center=center, axis=axis, method=method
-        )
+        return Expanding(self, min_periods=min_periods, axis=axis, method=method)
 
     @final
     @doc(ExponentialMovingWindow)

pandas/core/window/expanding.py

@@ -55,13 +55,6 @@ class Expanding(RollingAndExpandingMixin):
         Minimum number of observations in window required to have a value;
         otherwise, result is ``np.nan``.
 
-    center : bool, default False
-        If False, set the window labels as the right edge of the window index.
-
-        If True, set the window labels as the center of the window index.
-
-        .. deprecated:: 1.1.0
-
     axis : int or str, default 0
         If ``0`` or ``'index'``, roll across the rows.
 
@@ -123,21 +116,19 @@ class Expanding(RollingAndExpandingMixin):
     4  7.0
     """
 
-    _attributes: list[str] = ["min_periods", "center", "axis", "method"]
+    _attributes: list[str] = ["min_periods", "axis", "method"]
 
     def __init__(
         self,
         obj: NDFrame,
         min_periods: int = 1,
-        center: bool | None = None,
         axis: Axis = 0,
         method: str = "single",
         selection=None,
     ) -> None:
         super().__init__(
             obj=obj,
             min_periods=min_periods,
-            center=center,
             axis=axis,
             method=method,
             selection=selection,

pandas/tests/window/test_expanding.py

@@ -23,24 +23,16 @@ def test_doc_string():
     df.expanding(2).sum()
 
 
-@pytest.mark.filterwarnings(
-    "ignore:The `center` argument on `expanding` will be removed in the future"
-)
 def test_constructor(frame_or_series):
     # GH 12669
 
     c = frame_or_series(range(5)).expanding
 
     # valid
     c(min_periods=1)
-    c(min_periods=1, center=True)
-    c(min_periods=1, center=False)
 
 
 @pytest.mark.parametrize("w", [2.0, "foo", np.array([2])])
-@pytest.mark.filterwarnings(
-    "ignore:The `center` argument on `expanding` will be removed in the future"
-)
 def test_constructor_invalid(frame_or_series, w):
     # not valid
 
@@ -49,10 +41,6 @@ def test_constructor_invalid(frame_or_series, w):
     with pytest.raises(ValueError, match=msg):
         c(min_periods=w)
 
-    msg = "center must be a boolean"
-    with pytest.raises(ValueError, match=msg):
-        c(min_periods=1, center=w)
-
 
 @pytest.mark.parametrize("method", ["std", "mean", "sum", "max", "min", "var"])
 def test_numpy_compat(method):
@@ -241,18 +229,12 @@ def test_iter_expanding_series(ser, expected, min_periods):
         tm.assert_series_equal(actual, expected)
 
 
-def test_center_deprecate_warning():
+def test_center_invalid():
     # GH 20647
     df = DataFrame()
-    with tm.assert_produces_warning(FutureWarning):
+    with pytest.raises(TypeError, match=".* got an unexpected keyword"):
         df.expanding(center=True)
 
-    with tm.assert_produces_warning(FutureWarning):
-        df.expanding(center=False)
-
-    with tm.assert_produces_warning(None):
-        df.expanding()
-
 
 def test_expanding_sem(frame_or_series):
     # GH: 26476