Revised constraints and algorithm. Added comment denoting key/value for each dictionary in the code section.

graphs_trees/templates/test_foo.py

@@ -0,0 +1,19 @@
+from nose.tools import assert_equal
+
+
+class TestFoo(object):
+
+    def test_foo(self):
+        assert_equal(foo(None), None)
+        assert_equal(foo(0), 0)
+        assert_equal(foo('bar'), 'bar')
+        print('Success: test_foo')
+
+        
+def main():
+    test = TestFoo()
+    test.test_foo()
+
+    
+if __name__ == '__main__':
+    main()