Add test to verify a single period is not accepted as input

common/lib/calc/calc.py

@@ -182,7 +182,7 @@ def evaluator(variables, functions, string, cs=False):
 
     number_part = Word(nums)
 
-    # 0.33 or 7 or .34
+    # 0.33 or 7 or .34 or 16.
     inner_number = (number_part + Optional("." + Optional(number_part))) | ("." + number_part)
 
     # 0.33k or -17

common/lib/calc/tests/test_calc.py

@@ -37,6 +37,13 @@ class EvaluatorTest(unittest.TestCase):
         self.assertEqual(easy_eval("-3.14"), -3.14)
         self.assertEqual(easy_eval("-.618033989"), -0.618033989)
 
+    def test_period(self):
+        """
+        The string '.' should not evaluate to anything.
+        """
+        self.assertRaises(ParseException, calc.evaluator, {}, {}, '.')
+        self.assertRaises(ParseException, calc.evaluator, {}, {}, '1+.')
+
     def test_trailing_period(self):
         """
         Test that things like '4.' will be 4 and not throw an error