BUG: DataFrame.eval inconsistently handles duplicated columns

doc/source/whatsnew/v3.1.0.rst

@@ -393,6 +393,7 @@ Styler
 Other
 ^^^^^
 
+- Bug in :meth:`DataFrame.eval` where a column name appearing on multiple columns was resolved to a single column (yielding a :class:`Series`), inconsistent with :func:`pandas.eval` using ``resolvers=(df,)`` and with :meth:`DataFrame.__getitem__`, which include every column with that label (:issue:`65588`)
 - Bug in :meth:`Series.transform` and :meth:`DataFrame.transform` where passing a list of duplicate function names did not raise :class:`errors.SpecificationError` (:issue:`54929`)
 
 .. ***DO NOT USE THIS SECTION***

pandas/core/generic.py

@@ -575,7 +575,7 @@ def _get_index_resolvers(self) -> dict[Hashable, Series | MultiIndex]:
         return {clean_column_name(k): v for k, v in d.items() if not isinstance(k, int)}
 
     @final
-    def _get_cleaned_column_resolvers(self) -> dict[Hashable, Series]:
+    def _get_cleaned_column_resolvers(self) -> dict[Hashable, Series | DataFrame]:
         """
         Return the special character free column resolvers of a DataFrame.
 
@@ -590,17 +590,21 @@ def _get_cleaned_column_resolvers(self) -> dict[Hashable, Series]:
             return {clean_column_name(self.name): self}
 
         dtypes = self.dtypes
-        return {
-            clean_column_name(k): Series(
-                v, copy=False, index=self.index, name=k, dtype=dtype
-            ).__finalize__(self)
-            for k, v, dtype in zip(
-                self.columns,
-                self._iter_column_arrays(),
-                dtypes,
-                strict=True,
-            )
-        }
+        result: dict[Hashable, Series | DataFrame] = {}
+        for k, v, dtype in zip(
+            self.columns,
+            self._iter_column_arrays(),
+            dtypes,
+            strict=True,
+        ):
+            clean_key = clean_column_name(k)
+            if clean_key in result:
+                result[clean_key] = self[k]
+            else:
+                result[clean_key] = Series(
+                    v, copy=False, index=self.index, name=k, dtype=dtype
+                ).__finalize__(self)
+        return result
 
     @final
     @property

pandas/tests/frame/test_query_eval.py

@@ -170,6 +170,17 @@ def test_query_duplicate_column_name(self, engine, parser):
 
         tm.assert_frame_equal(res, expect)
 
+    def test_eval_duplicate_column_name(self, engine, parser):
+        # GH#65588
+        df = DataFrame({"a": range(3), "b": range(10, 13), "c": range(3)}).rename(
+            columns={"b": "a"}
+        )
+
+        result = df.eval("a == 1", engine=engine, parser=parser)
+        expected = pd.eval("a == 1", resolvers=(df,), engine=engine, parser=parser)
+
+        tm.assert_frame_equal(result, expected)
+
     def test_eval_resolvers_as_list(self):
         # GH 14095
         df = DataFrame(