--- /dev/null	Thu Jan 01 00:00:00 1970 +0000
+++ b/test/test_pythonexpr.py	Tue Mar 26 17:31:28 2019 -0400
@@ -0,0 +1,30 @@
+"""
+In Python 3, sometimes TAL "python:" expressions that refer to
+variables but not all variables are recognized. That is in Python 2.7
+all variables used in a TAL "python:" expression are recognized as
+references. In Python 3.5 (perhaps earlier), some TAL "python:"
+expressions refer to variables but the reference generates an error
+like this:
+
+<class 'NameError'>: name 'some_tal_variable' is not defined
+
+even when the variable is defined. Output after this message lists the
+variable and its value.
+"""
+
+import unittest
+
+from roundup.cgi.PageTemplates.PythonExpr import PythonExpr as PythonExprClass
+
+class ExprTest(unittest.TestCase):
+    def testExpr(self):
+        expr = '[x for x in context.assignedto ' \
+               'if x.realname not in user_realnames]'
+        pe = PythonExprClass('test', expr, None)
+        # Looking at the expression, only context and user_realnames are
+        # external variables. The names assignedto and realname are members,
+        # and x is local.
+        required_names = ['context', 'user_realnames']
+        got_names = pe._f_varnames
+        for required_name in required_names:
+            self.assertIn(required_name, got_names)