BUG: do not remove temporaries from eval/query scope

doc/source/v0.14.1.txt

@@ -71,3 +71,6 @@ Bug Fixes
   and ``left`` keyword is specified (:issue:`7226`)
 - BUG in ``DataFrame.hist`` raises ``TypeError`` when it contains non numeric column (:issue:`7277`)
 - BUG in ``Index.delete`` does not preserve ``name`` and ``freq`` attributes (:issue:`7302`)
+- Bug in ``DataFrame.query()``/``eval`` where local string variables with the @
+  sign were being treated as temporaries attempting to be deleted
+  (:issue:`7300`).

pandas/computation/expr.py

@@ -340,12 +340,10 @@ def _rewrite_membership_op(self, node, left, right):
             # pop the string variable out of locals and replace it with a list
             # of one string, kind of a hack
             if right_str:
-                self.env.remove_tmp(right.name)
                 name = self.env.add_tmp([right.value])
                 right = self.term_type(name, self.env)
 
             if left_str:
-                self.env.remove_tmp(left.name)
                 name = self.env.add_tmp([left.value])
                 left = self.term_type(name, self.env)
 

pandas/computation/scope.py

@@ -278,16 +278,6 @@ def add_tmp(self, value):
         # only increment if the variable gets put in the scope
         return name
 
-    def remove_tmp(self, name):
-        """Remove a temporary variable from this scope
-
-        Parameters
-        ----------
-        name : str
-            The name of a temporary to be removed
-        """
-        del self.temps[name]
-
     @property
     def ntemps(self):
         """The number of temporary variables in this scope"""

pandas/tests/test_frame.py

@@ -13685,6 +13685,18 @@ def test_query_single_element_booleans(self):
         for parser, engine in product(PARSERS, ENGINES):
             yield self.check_query_single_element_booleans, parser, engine
 
+    def check_query_string_scalar_variable(self, parser, engine):
+        tm.skip_if_no_ne(engine)
+        df = pd.DataFrame({'Symbol': ['BUD US', 'BUD US', 'IBM US', 'IBM US'],
+                           'Price': [109.70, 109.72, 183.30, 183.35]})
+        e = df[df.Symbol == 'BUD US']
+        symb = 'BUD US'
+        r = df.query('Symbol == @symb', parser=parser, engine=engine)
+        tm.assert_frame_equal(e, r)
+
+    def test_query_string_scalar_variable(self):
+        for parser, engine in product(['pandas'], ENGINES):
+            yield self.check_query_string_scalar_variable, parser, engine
 
 class TestDataFrameEvalNumExprPandas(tm.TestCase):