Backport PR pandas-dev#47085 on branch 1.4.x (BUG: Eval scopes ignoring empty dictionaries (pandas-dev#47084)) (pandas-dev#47250)

Backport PR pandas-dev#47085: BUG: Eval scopes ignoring empty dictionaries (pandas-dev#47084)

Co-authored-by: Alex-Blade <[email protected]>

Author: meeseeksmachine

doc/source/whatsnew/v1.4.3.rst

@@ -31,6 +31,7 @@ Fixed regressions
 
 Bug fixes
 ~~~~~~~~~
+- Bug in :meth:`pd.eval`, :meth:`DataFrame.eval` and :meth:`DataFrame.query` where passing empty ``local_dict`` or ``global_dict`` was treated as passing ``None`` (:issue:`47084`)
 - Most I/O methods do no longer suppress ``OSError`` and ``ValueError`` when closing file handles (:issue:`47136`)
 -
 

pandas/core/computation/pytables.py

@@ -563,7 +563,7 @@ def __init__(
         self._visitor = None
 
         # capture the environment if needed
-        local_dict: DeepChainMap[Any, Any] = DeepChainMap()
+        local_dict: DeepChainMap[Any, Any] | None = None
 
         if isinstance(where, PyTablesExpr):
             local_dict = where.env.scope

pandas/core/computation/scope.py

@@ -133,11 +133,13 @@ def __init__(
             # shallow copy here because we don't want to replace what's in
             # scope when we align terms (alignment accesses the underlying
             # numpy array of pandas objects)
-            scope_global = self.scope.new_child((global_dict or frame.f_globals).copy())
+            scope_global = self.scope.new_child(
+                (global_dict if global_dict is not None else frame.f_globals).copy()
+            )
             self.scope = DeepChainMap(scope_global)
             if not isinstance(local_dict, Scope):
                 scope_local = self.scope.new_child(
-                    (local_dict or frame.f_locals).copy()
+                    (local_dict if local_dict is not None else frame.f_locals).copy()
                 )
                 self.scope = DeepChainMap(scope_local)
         finally:

pandas/tests/computation/test_eval.py

@@ -43,6 +43,7 @@
 from pandas.core.computation.ops import (
     ARITH_OPS_SYMS,
     SPECIAL_CASE_ARITH_OPS_SYMS,
+    UndefinedVariableError,
     _binary_math_ops,
     _binary_ops_dict,
     _unary_math_ops,
@@ -1747,6 +1748,20 @@ def test_no_new_globals(self, engine, parser):
         gbls2 = globals().copy()
         assert gbls == gbls2
 
+    def test_empty_locals(self, engine, parser):
+        # GH 47084
+        x = 1  # noqa: F841
+        msg = "name 'x' is not defined"
+        with pytest.raises(UndefinedVariableError, match=msg):
+            pd.eval("x + 1", engine=engine, parser=parser, local_dict={})
+
+    def test_empty_globals(self, engine, parser):
+        # GH 47084
+        msg = "name '_var_s' is not defined"
+        e = "_var_s * 2"
+        with pytest.raises(UndefinedVariableError, match=msg):
+            pd.eval(e, engine=engine, parser=parser, global_dict={})
+
 
 @td.skip_if_no_ne
 def test_invalid_engine():