Merge remote-tracking branch 'upstream/main' into sty/ruff

doc/source/whatsnew/v2.2.1.rst

@@ -13,7 +13,9 @@ including other versions of pandas.
 
 Fixed regressions
 ~~~~~~~~~~~~~~~~~
+- Fixed performance regression in :meth:`Series.combine_first` (:issue:`55845`)
 - Fixed regression in :func:`merge_ordered` raising ``TypeError`` for ``fill_method="ffill"`` and ``how="left"`` (:issue:`57010`)
+- Fixed regression in :meth:`Series.pct_change` raising a ``ValueError`` for an empty :class:`Series` (:issue:`57056`)
 
 .. ---------------------------------------------------------------------------
 .. _whatsnew_221.bug_fixes:

pandas/compat/numpy/function.py

@@ -138,6 +138,7 @@ def validate_argmax_with_skipna(skipna: bool | ndarray | None, args, kwargs) ->
 ARGSORT_DEFAULTS["kind"] = "quicksort"
 ARGSORT_DEFAULTS["order"] = None
 ARGSORT_DEFAULTS["kind"] = None
+ARGSORT_DEFAULTS["stable"] = None
 
 
 validate_argsort = CompatValidator(
@@ -149,6 +150,7 @@ def validate_argmax_with_skipna(skipna: bool | ndarray | None, args, kwargs) ->
 ARGSORT_DEFAULTS_KIND: dict[str, int | None] = {}
 ARGSORT_DEFAULTS_KIND["axis"] = -1
 ARGSORT_DEFAULTS_KIND["order"] = None
+ARGSORT_DEFAULTS_KIND["stable"] = None
 validate_argsort_kind = CompatValidator(
     ARGSORT_DEFAULTS_KIND, fname="argsort", max_fname_arg_count=0, method="both"
 )

pandas/core/generic.py

@@ -12274,19 +12274,20 @@ def pct_change(
             if limit is lib.no_default:
                 cols = self.items() if self.ndim == 2 else [(None, self)]
                 for _, col in cols:
-                    mask = col.isna().values
-                    mask = mask[np.argmax(~mask) :]
-                    if mask.any():
-                        warnings.warn(
-                            "The default fill_method='pad' in "
-                            f"{type(self).__name__}.pct_change is deprecated and will "
-                            "be removed in a future version. Either fill in any "
-                            "non-leading NA values prior to calling pct_change or "
-                            "specify 'fill_method=None' to not fill NA values.",
-                            FutureWarning,
-                            stacklevel=find_stack_level(),
-                        )
-                        break
+                    if len(col) > 0:
+                        mask = col.isna().values
+                        mask = mask[np.argmax(~mask) :]
+                        if mask.any():
+                            warnings.warn(
+                                "The default fill_method='pad' in "
+                                f"{type(self).__name__}.pct_change is deprecated and "
+                                "will be removed in a future version. Either fill in "
+                                "any non-leading NA values prior to calling pct_change "
+                                "or specify 'fill_method=None' to not fill NA values.",
+                                FutureWarning,
+                                stacklevel=find_stack_level(),
+                            )
+                            break
             fill_method = "pad"
         if limit is lib.no_default:
             limit = None

pandas/core/indexes/base.py

@@ -958,7 +958,7 @@ def __array_ufunc__(self, ufunc: np.ufunc, method: str_t, *inputs, **kwargs):
         return self.__array_wrap__(result)
 
     @final
-    def __array_wrap__(self, result, context=None):
+    def __array_wrap__(self, result, context=None, return_scalar=False):
         """
         Gets called after a ufunc and other functions e.g. np.split.
         """

pandas/core/series.py

@@ -87,6 +87,7 @@
 from pandas.core.dtypes.dtypes import (
     CategoricalDtype,
     ExtensionDtype,
+    SparseDtype,
 )
 from pandas.core.dtypes.generic import (
     ABCDataFrame,
@@ -3520,6 +3521,13 @@ def combine_first(self, other) -> Series:
         """
         from pandas.core.reshape.concat import concat
 
+        if self.dtype == other.dtype:
+            if self.index.equals(other.index):
+                return self.mask(self.isna(), other)
+            elif self._can_hold_na and not isinstance(self.dtype, SparseDtype):
+                this, other = self.align(other, join="outer")
+                return this.mask(this.isna(), other)
+
         new_index = self.index.union(other.index)
 
         this = self
@@ -4076,6 +4084,7 @@ def argsort(
         axis: Axis = 0,
         kind: SortKind = "quicksort",
         order: None = None,
+        stable: None = None,
     ) -> Series:
         """
         Return the integer indices that would sort the Series values.
@@ -4092,6 +4101,8 @@ def argsort(
             information. 'mergesort' and 'stable' are the only stable algorithms.
         order : None
             Has no effect but is accepted for compatibility with numpy.
+        stable : None
+            Has no effect but is accepted for compatibility with numpy.
 
         Returns
         -------

pandas/tests/series/methods/test_pct_change.py

@@ -118,3 +118,11 @@ def test_pct_change_no_warning_na_beginning():
     result = ser.pct_change()
     expected = Series([np.nan, np.nan, np.nan, 1, 0.5])
     tm.assert_series_equal(result, expected)
+
+
+def test_pct_change_empty():
+    # GH 57056
+    ser = Series([], dtype="float64")
+    expected = ser.copy()
+    result = ser.pct_change(periods=0)
+    tm.assert_series_equal(expected, result)