prohibit apply and applymap in non-unique case

pandas-dev · jreback · May 6, 2021 · May 2, 2021 · May 2, 2021 · May 2, 2021
commit 4faeb29e1bc2085231bfa6915760fee9898335fc
diff --git a/pandas/io/formats/style.py b/pandas/io/formats/style.py
@@ -472,26 +472,19 @@ def _update_ctx(self, attrs: DataFrame) -> None:
             Whitespace shouldn't matter and the final trailing ';' shouldn't
             matter.
         """
-        err = KeyError(
-            "`Styler.apply` and `.applymap` are not compatible with subset slices "
-            "containing non-unique index or column keys."
-        )
+        if not self.index.is_unique or not self.columns.is_unique:
+            raise KeyError(
+                "`Styler.apply` and `.applymap` are not compatible "
+                "with non-unique index or columns."
+            )
 
         for cn in attrs.columns:
-            try:
-                for rn, c in attrs[[cn]].itertuples():
-                    if not c:
-                        continue
-                    css_list = maybe_convert_css_to_tuples(c)
-                    i, j = self.index.get_loc(rn), self.columns.get_loc(cn)
-                    self.ctx[(i, j)].extend(css_list)
-            except ValueError as ve:
-                if "Styles supplied as string must follow CSS rule formats" in str(ve):
-                    raise ve  # error is from maybe_convert_css_to_tuples()
-                else:
-                    raise err  # 'too many values to unpack': caught non-unique column
-            except TypeError:
-                raise err  # 'unhashable type: slice' caught a non-unique index
+            for rn, c in attrs[[cn]].itertuples():
+                if not c:
+                    continue
+                css_list = maybe_convert_css_to_tuples(c)
+                i, j = self.index.get_loc(rn), self.columns.get_loc(cn)
+                self.ctx[(i, j)].extend(css_list)
 
     def _copy(self, deepcopy: bool = False) -> Styler:
         styler = Styler(

diff --git a/pandas/tests/io/formats/style/test_non_unique.py b/pandas/tests/io/formats/style/test_non_unique.py
@@ -52,15 +52,7 @@ def test_apply_applymap_non_unique_raises(df, func):
         op = lambda v: "color: red;"
 
     with pytest.raises(KeyError, match="`Styler.apply` and `.applymap` are not"):
-        # slice is non-unique on columns
-        getattr(df.style, func)(op, subset=("i", "d"))._compute()
-
-    with pytest.raises(KeyError, match="`Styler.apply` and `.applymap` are not"):
-        # slice is non-unique on rows
-        getattr(df.style, func)(op, subset=("j", "c"))._compute()
-
-    # unique subset OK
-    getattr(df.style, func)(op, subset=("i", "c"))._compute()
+        getattr(df.style, func)(op)._compute()
 
 
 def test_table_styles_dict_non_unique_index(styler):
@@ -83,12 +75,6 @@ def test_table_styles_dict_non_unique_columns(styler):
     ]
 
 
-def test_maybe_convert_css_raises(styler):
-    # test _update_ctx() detects the right ValueError where non-unique columns present
-    with pytest.raises(ValueError, match="Styles supplied as string must follow CSS"):
-        styler.applymap(lambda x: "bad-css;")._compute()
-
-
 def test_tooltips_non_unique_raises(styler):
     # ttips has unique keys
     ttips = DataFrame([["1", "2"], ["3", "4"]], columns=["c", "d"], index=["a", "b"])