BUG: Fixed strange behaviour of pd.DataFrame.drop() with inplace argu… (

#30501)

doc/source/whatsnew/v1.1.0.rst

@@ -411,6 +411,7 @@ Reshaping
 - Bug in :func:`concat` where the resulting indices are not copied when ``copy=True`` (:issue:`29879`)
 - :meth:`Series.append` will now raise a ``TypeError`` when passed a DataFrame or a sequence containing Dataframe (:issue:`31413`)
 - :meth:`DataFrame.replace` and :meth:`Series.replace` will raise a ``TypeError`` if ``to_replace`` is not an expected type. Previously the ``replace`` would fail silently (:issue:`18634`)
+- Bug on inplace operation of a Series that was adding a column to the DataFrame from where it was originally dropped from (using inplace=True) (:issue:`30484`)
 - Bug in :meth:`DataFrame.apply` where callback was called with :class:`Series` parameter even though ``raw=True`` requested. (:issue:`32423`)
 - Bug in :meth:`DataFrame.pivot_table` losing timezone information when creating a :class:`MultiIndex` level from a column with timezone-aware dtype (:issue:`32558`)
 - Bug in :meth:`concat` where when passing a non-dict mapping as ``objs`` would raise a ``TypeError`` (:issue:`32863`)

pandas/core/ops/methods.py

@@ -93,7 +93,8 @@ def _wrap_inplace_method(method):
 
         def f(self, other):
             result = method(self, other)
-
+            # Delete cacher
+            self._reset_cacher()
             # this makes sure that we are aligned like the input
             # we are updating inplace so we want to ignore is_copy
             self._update_inplace(

pandas/tests/frame/test_axis_select_reindex.py

@@ -716,3 +716,24 @@ def test_reindex_multi_categorical_time(self):
         result = df2.reindex(midx)
         expected = pd.DataFrame({"a": [0, 1, 2, 3, 4, 5, 6, np.nan, 8]}, index=midx)
         tm.assert_frame_equal(result, expected)
+
+    @pytest.mark.parametrize(
+        "operation", ["__iadd__", "__isub__", "__imul__", "__ipow__"]
+    )
+    @pytest.mark.parametrize("inplace", [False, True])
+    def test_inplace_drop_and_operation(self, operation, inplace):
+        # GH 30484
+        df = pd.DataFrame({"x": range(5)})
+        expected = df.copy()
+        df["y"] = range(5)
+        y = df["y"]
+
+        with tm.assert_produces_warning(None):
+            if inplace:
+                df.drop("y", axis=1, inplace=inplace)
+            else:
+                df = df.drop("y", axis=1, inplace=inplace)
+
+            # Perform operation and check result
+            getattr(y, operation)(1)
+            tm.assert_frame_equal(df, expected)