BUG: UndefinedVariableError in DataFrame.query with classname

doc/source/whatsnew/v1.5.2.rst

@@ -13,6 +13,7 @@ including other versions of pandas.
 
 Fixed regressions
 ~~~~~~~~~~~~~~~~~
+- Fixed regression in :meth:`DataFrame.query` raising ``UndefinedVariableError`` when calling it with class as a name (:issue:`48694`)
 - Fixed regression in :meth:`MultiIndex.join` for extension array dtypes (:issue:`49277`)
 - Fixed regression in :meth:`Series.replace` raising ``RecursionError`` with numeric dtype and when specifying ``value=None`` (:issue:`45725`)
 - Fixed regression in arithmetic operations for :class:`DataFrame` with :class:`MultiIndex` columns with different dtypes (:issue:`49769`)

pandas/core/computation/ops.py

@@ -29,6 +29,7 @@
     result_type_many,
 )
 from pandas.core.computation.scope import DEFAULT_GLOBALS
+from pandas.core.series import Series
 
 from pandas.io.formats.printing import (
     pprint_thing,
@@ -102,10 +103,9 @@ def evaluate(self, *args, **kwargs) -> Term:
     def _resolve_name(self):
         local_name = str(self.local_name)
         is_local = self.is_local
-        if local_name in self.env.scope and isinstance(
-            self.env.scope[local_name], type
-        ):
-            is_local = False
+        check = self.env.scope.get("column") == local_name
+        if not isinstance(check, Series) and check:
+            is_local = not is_local
 
         res = self.env.resolve(local_name, is_local=is_local)
         self.update(res)

pandas/core/computation/pytables.py

@@ -609,20 +609,21 @@ def __repr__(self) -> str:
 
     def evaluate(self):
         """create and return the numexpr condition and filter"""
-        try:
-            self.condition = self.terms.prune(ConditionBinOp)
-        except AttributeError as err:
-            raise ValueError(
-                f"cannot process expression [{self.expr}], [{self}] "
-                "is not a valid condition"
-            ) from err
-        try:
-            self.filter = self.terms.prune(FilterBinOp)
-        except AttributeError as err:
-            raise ValueError(
-                f"cannot process expression [{self.expr}], [{self}] "
-                "is not a valid filter"
-            ) from err
+        if self.terms is not None:
+            try:
+                self.condition = self.terms.prune(ConditionBinOp)
+            except AttributeError as err:
+                raise ValueError(
+                    f"cannot process expression [{self.expr}], [{self}] "
+                    "is not a valid condition"
+                ) from err
+            try:
+                self.filter = self.terms.prune(FilterBinOp)
+            except AttributeError as err:
+                raise ValueError(
+                    f"cannot process expression [{self.expr}], [{self}] "
+                    "is not a valid filter"
+                ) from err
 
         return self.condition, self.filter
 

pandas/tests/computation/test_eval.py

@@ -1846,7 +1846,7 @@ def test_negate_lt_eq_le(engine, parser):
 )
 def test_eval_no_support_column_name(request, column):
     # GH 44603
-    if column in ["True", "False", "inf", "Inf"]:
+    if column in ["True", "False"]:
         request.node.add_marker(
             pytest.mark.xfail(
                 raises=KeyError,
@@ -1861,6 +1861,17 @@ def test_eval_no_support_column_name(request, column):
     tm.assert_frame_equal(result, expected)
 
 
+def test_classname_frame_query():
+    # GH 48694
+    class A:
+        a = 1
+
+    df1 = DataFrame({"x": [1, 2, 3], "y": [4, 5, 6]})
+    df_test = DataFrame({"x": [1], "y": [4]})
+    tm.assert_frame_equal(df_test, df1.query(f"x=={A.a}"))
+    tm.assert_frame_equal(df_test, df1.query("[email protected]"))
+
+
 @td.skip_array_manager_not_yet_implemented
 def test_set_inplace(using_copy_on_write):
     # https://github.com/pandas-dev/pandas/issues/47449