BUG: overriden methods of subclasses of Styler are not called during rendering #52728

doc/source/whatsnew/v2.1.0.rst

@@ -409,7 +409,7 @@ ExtensionArray
 
 Styler
 ^^^^^^
--
+- Bug in :meth:`Styler._copy` calling overridden methods in subclasses of :class:`Styler` (:issue:`52728`)
 -
 
 Other

pandas/io/formats/style.py

@@ -1056,7 +1056,9 @@ def to_latex(
 
         .. figure:: ../../_static/style/latex_stocks.png
         """
-        obj = self._copy(deepcopy=True)  # manipulate table_styles on obj, not self
+        obj = Styler._copy(
+            self, deepcopy=True
+        )  # manipulate table_styles on obj, not self
 
         table_selectors = (
             [style["selector"] for style in self.table_styles]
@@ -1292,7 +1294,9 @@ def to_html(
         --------
         DataFrame.to_html: Write a DataFrame to a file, buffer or string in HTML format.
         """
-        obj = self._copy(deepcopy=True)  # manipulate table_styles on obj, not self
+        obj = Styler._copy(
+            self, deepcopy=True
+        )  # manipulate table_styles on obj, not self
 
         if table_uuid:
             obj.set_uuid(table_uuid)
@@ -1404,7 +1408,7 @@ def to_string(
         str or None
             If `buf` is None, returns the result as a string. Otherwise returns `None`.
         """
-        obj = self._copy(deepcopy=True)
+        obj = Styler._copy(self, deepcopy=True)
 
         if sparse_index is None:
             sparse_index = get_option("styler.sparse.index")
@@ -1554,7 +1558,8 @@ def _update_ctx_header(self, attrs: DataFrame, axis: AxisInt) -> None:
                 else:
                     self.ctx_columns[(j, i)].extend(css_list)
 
-    def _copy(self, deepcopy: bool = False) -> Styler:
+    @classmethod
+    def _copy(cls, self, deepcopy: bool = False) -> Styler:
         """
         Copies a Styler, allowing for deepcopy or shallow copy
 
@@ -1578,8 +1583,8 @@ def _copy(self, deepcopy: bool = False) -> Styler:
           - applied styles (_todo)
 
         """
-        # GH 40675
-        styler = Styler(
+        # GH 40675, 52728
+        styler = type(self)(
             self.data,  # populates attributes 'data', 'columns', 'index' as shallow
         )
         shallow = [  # simple string or boolean immutables
@@ -1624,10 +1629,10 @@ def _copy(self, deepcopy: bool = False) -> Styler:
         return styler
 
     def __copy__(self) -> Styler:
-        return self._copy(deepcopy=False)
+        return Styler._copy(self, deepcopy=False)
 
     def __deepcopy__(self, memo) -> Styler:
-        return self._copy(deepcopy=True)
+        return Styler._copy(self, deepcopy=True)
 
     def clear(self) -> None:
         """

pandas/tests/io/formats/style/test_style.py

@@ -45,7 +45,7 @@ def mi_styler(mi_df):
 @pytest.fixture
 def mi_styler_comp(mi_styler):
     # comprehensively add features to mi_styler
-    mi_styler = mi_styler._copy(deepcopy=True)
+    mi_styler = Styler._copy(mi_styler, deepcopy=True)
     mi_styler.css = {**mi_styler.css, "row": "ROW", "col": "COL"}
     mi_styler.uuid_len = 5
     mi_styler.uuid = "abcde"
@@ -313,6 +313,20 @@ def test_copy(comprehensive, render, deepcopy, mi_styler, mi_styler_comp):
                 assert id(getattr(s2, attr)) != id(getattr(styler, attr))
 
 
+@pytest.mark.parametrize("deepcopy", [True, False])
+def test_inherited_copy(mi_styler, deepcopy):
+    # Ensure that the inherited class is preserved when a Styler object is copied.
+    # GH 52728
+    class CustomStyler(Styler):
+        pass
+
+    custom_styler = CustomStyler(mi_styler.data)
+    custom_styler_copy = (
+        copy.deepcopy(custom_styler) if deepcopy else copy.copy(custom_styler)
+    )
+    assert isinstance(custom_styler_copy, CustomStyler)
+
+
 def test_clear(mi_styler_comp):
     # NOTE: if this test fails for new features then 'mi_styler_comp' should be updated
     # to ensure proper testing of the 'copy', 'clear', 'export' methods with new feature

pandas/tests/io/formats/style/test_to_latex.py

@@ -605,7 +605,7 @@ def test_parse_latex_css_conversion_option():
 
 def test_styler_object_after_render(styler):
     # GH 42320
-    pre_render = styler._copy(deepcopy=True)
+    pre_render = Styler._copy(styler, deepcopy=True)
     styler.to_latex(
         column_format="rllr",
         position="h",