OrangeDataFrame: Fix patched constructor

This is a proper solution that would work before and would continue
to work in pandas>=3 -- if it was not for a bug in pandas
(pandas-dev/pandas#59913).

Hence, this commit also (dynamically) patches the bug in pandas.

Orange/data/pandas_compat.py

@@ -1,11 +1,12 @@
 """Pandas DataFrame↔Table conversion helpers"""
-from unittest.mock import patch
+from functools import partial
 
 import numpy as np
 from scipy import sparse as sp
 from scipy.sparse import csr_matrix
 import pandas as pd
 from pandas.core.arrays import SparseArray
+import pandas.core.arrays.sparse.accessor
 from pandas.api.types import (
     is_object_dtype,
     is_datetime64_any_dtype,
@@ -22,6 +23,19 @@
 __all__ = ['table_from_frame', 'table_to_frame']
 
 
+# Patch a bug in pandas SparseFrameAccessor.to_dense
+# As of pandas=3.0.0.dev0+1524.g23c497bb2f, to_dense ignores _constructor
+# and alwats returns DataFrame.
+# Remove this if https://github.com/pandas-dev/pandas/issues/59913 is fixed
+def to_dense(self):
+    # pylint: disable=protected-access
+    data = {k: v.array.to_dense() for k, v in self._parent.items()}
+    constr = self._parent._constructor
+    return constr(data, index=self._parent.index, columns=self._parent.columns)
+
+pandas.core.arrays.sparse.accessor.SparseFrameAccessor.to_dense = to_dense
+
+
 class OrangeDataFrame(pd.DataFrame):
     _metadata = ["orange_variables", "orange_weights",
                  "orange_attributes", "orange_role"]
@@ -74,8 +88,6 @@ def __init__(self, *args, **kwargs):
             data = dict(enumerate(sparrays))
             super().__init__(data, index=index, **kwargs)
             self.columns = columns
-            # a hack to keep Orange df _metadata in sparse->dense conversion
-            self.sparse.to_dense = self.__patch_constructor(self.sparse.to_dense)
         else:
             copy = kwargs.pop("copy", False)
             super().__init__(
@@ -88,21 +100,15 @@ def __init__(self, *args, **kwargs):
                                if table.W.size > 0 else {})
         self.orange_attributes = table.attributes
 
-    def __patch_constructor(self, method):
-        def new_method(*args, **kwargs):
-            with patch(
-                    'pandas.DataFrame',
-                    OrangeDataFrame
-            ):
-                df = method(*args, **kwargs)
-            df.__finalize__(self)
-            return df
-
-        return new_method
-
     @property
     def _constructor(self):
-        return OrangeDataFrame
+        return partial(self.from_existing, self)
+
+    @staticmethod
+    def from_existing(existing, *args, **kwargs):
+        self = type(existing)(*args, **kwargs)
+        self.__finalize__(existing)
+        return self
 
     def to_orange_table(self):
         return table_from_frame(self)

Orange/data/tests/test_pandas.py

@@ -19,6 +19,11 @@
     pytz = None
 
 class TestPandasCompat(unittest.TestCase):
+    def test_patch_for_to_dense(self):
+        if pd.__version__ >= "3" and "dev" not in pd.__version__:
+            self.fail("Try removing the patch for to_dense in pandas_compat.\n"
+                      "If successful, remove this test.")
+
     def test_table_from_frame(self):
         nan = np.nan
         df = pd.DataFrame([['a', 1, pd.Timestamp('2017-12-19')],