DEPR: is_copy arg of take (pandas-dev#30615)

doc/source/whatsnew/v1.0.0.rst

@@ -579,6 +579,7 @@ Deprecations
 - The deprecated internal attributes ``_start``, ``_stop`` and ``_step`` of :class:`RangeIndex` now raise a ``FutureWarning`` instead of a ``DeprecationWarning`` (:issue:`26581`)
 - The ``pandas.util.testing`` module has been deprecated. Use the public API in ``pandas.testing`` documented at :ref:`api.general.testing` (:issue:`16232`).
 - ``pandas.SparseArray`` has been deprecated.  Use ``pandas.arrays.SparseArray`` (:class:`arrays.SparseArray`) instead. (:issue:`30642`)
+- The parameter ``is_copy`` of :meth:`DataFrame.take` has been deprecated and will be removed in a future version. (:issue:`27357`)
 
 **Selecting Columns from a Grouped DataFrame**
 

pandas/core/generic.py

@@ -3275,7 +3275,7 @@ def _clear_item_cache(self) -> None:
     # Indexing Methods
 
     def take(
-        self: FrameOrSeries, indices, axis=0, is_copy: bool_t = True, **kwargs
+        self: FrameOrSeries, indices, axis=0, is_copy: Optional[bool_t] = None, **kwargs
     ) -> FrameOrSeries:
         """
         Return the elements in the given *positional* indices along an axis.
@@ -3293,6 +3293,8 @@ def take(
             selecting rows, ``1`` means that we are selecting columns.
         is_copy : bool, default True
             Whether to return a copy of the original object or not.
+
+            .. deprecated:: 1.0.0
         **kwargs
             For compatibility with :meth:`numpy.take`. Has no effect on the
             output.
@@ -3351,6 +3353,16 @@ class  max_speed
         1  monkey  mammal        NaN
         3    lion  mammal       80.5
         """
+        if is_copy is not None:
+            warnings.warn(
+                "is_copy is deprecated and will be removed in a future version. "
+                "take will always return a copy in the future.",
+                FutureWarning,
+                stacklevel=2,
+            )
+        else:
+            is_copy = True
+
         nv.validate_take(tuple(), kwargs)
 
         self._consolidate_inplace()
@@ -5014,7 +5026,7 @@ def sample(
             )
 
         locs = rs.choice(axis_length, size=n, replace=replace, p=weights)
-        return self.take(locs, axis=axis, is_copy=False)
+        return self.take(locs, axis=axis)
 
     _shared_docs[
         "pipe"
@@ -7011,7 +7023,8 @@ def asof(self, where, subset=None):
 
         # mask the missing
         missing = locs == -1
-        data = self.take(locs, is_copy=False)
+        d = self.take(locs)
+        data = d.copy()
         data.index = where
         data.loc[missing] = np.nan
         return data if is_list else data.iloc[-1]

pandas/core/groupby/grouper.py

@@ -194,7 +194,7 @@ def _set_grouper(self, obj: FrameOrSeries, sort: bool = False):
             # use stable sort to support first, last, nth
             indexer = self.indexer = ax.argsort(kind="mergesort")
             ax = ax.take(indexer)
-            obj = obj.take(indexer, axis=self.axis, is_copy=False)
+            obj = obj.take(indexer, axis=self.axis)
 
         self.obj = obj
         self.grouper = ax

pandas/tests/frame/methods/test_asof.py

@@ -30,6 +30,7 @@ def test_basic(self, date_range_frame):
         ub = df.index[30]
 
         dates = list(dates)
+
         result = df.asof(dates)
         assert result.notna().all(1).all()
 
@@ -65,6 +66,7 @@ def test_missing(self, date_range_frame):
         # no match found - `where` value before earliest date in index
         N = 10
         df = date_range_frame.iloc[:N].copy()
+
         result = df.asof("1989-12-31")
 
         expected = Series(
@@ -132,5 +134,6 @@ def test_time_zone_aware_index(self, stamp, expected):
                 Timestamp("2018-01-01 22:35:10.550+00:00"),
             ],
         )
+
         result = df.asof(stamp)
         tm.assert_series_equal(result, expected)

pandas/tests/generic/test_generic.py

@@ -820,6 +820,18 @@ def test_take_invalid_kwargs(self):
             with pytest.raises(ValueError, match=msg):
                 obj.take(indices, mode="clip")
 
+    def test_depr_take_kwarg_is_copy(self):
+        # GH 27357
+        df = DataFrame({"A": [1, 2, 3]})
+        msg = (
+            "is_copy is deprecated and will be removed in a future version. "
+            "take will always return a copy in the future."
+        )
+        with tm.assert_produces_warning(FutureWarning) as w:
+            df.take([0, 1], is_copy=True)
+
+        assert w[0].message.args[0] == msg
+
     def test_equals(self):
         s1 = pd.Series([1, 2, 3], index=[0, 2, 1])
         s2 = s1.copy()