From ae69462463c9afe4c6c920391020a3f4cbbddd3f Mon Sep 17 00:00:00 2001
From: Phillip Cloud <cpcloud@gmail.com>
Date: Thu, 20 Feb 2014 23:57:59 -0500
Subject: [PATCH] BUG: correctly tokenize local variable references

---
 pandas/computation/expr.py | 8 +++++++-
 pandas/tests/test_frame.py | 8 ++++++++
 2 files changed, 15 insertions(+), 1 deletion(-)

diff --git a/pandas/computation/expr.py b/pandas/computation/expr.py
index 454a28fd82362..0f2b3e643d83c 100644
--- a/pandas/computation/expr.py
+++ b/pandas/computation/expr.py
@@ -57,7 +57,13 @@ def _replace_booleans(source):
 
 def _replace_locals(source, local_symbol='@'):
     """Replace local variables with a syntactically valid name."""
-    return source.replace(local_symbol, _LOCAL_TAG)
+    res = []
+    for toknum, tokval, _, _, _ in tokenize_string(source):
+        if toknum == tokenize.OP and tokval == local_symbol:
+            res.append((tokenize.OP, _LOCAL_TAG))
+        else:
+            res.append((toknum, tokval))
+    return tokenize.untokenize(res)
 
 
 def _preparse(source):
diff --git a/pandas/tests/test_frame.py b/pandas/tests/test_frame.py
index 88cf3179b33f2..8d15a06ad7baf 100644
--- a/pandas/tests/test_frame.py
+++ b/pandas/tests/test_frame.py
@@ -12774,6 +12774,14 @@ def test_local_variable_with_in(self):
         result = df.query('@b - 1 in a', engine=engine, parser=parser)
         tm.assert_frame_equal(expected, result)
 
+    def test_at_inside_string(self):
+        engine, parser = self.engine, self.parser
+        skip_if_no_pandas_parser(parser)
+        c = 1
+        df = DataFrame({'a': ['a', 'a', 'b', 'b', '@c', '@c']})
+        result = df.query('a == "@c"', engine=engine, parser=parser)
+        expected = df[df.a == "@c"]
+        tm.assert_frame_equal(result, expected)
 
 class TestDataFrameQueryNumExprPython(TestDataFrameQueryNumExprPandas):