Added instructions append for error handling, updated JinJa2 template and example, and regenerated test files.

Author: BethanyG

exercises/practice/hamming/.docs/instructions.append.md

@@ -0,0 +1,14 @@
+# Instructions append
+
+## Exception messages
+
+Sometimes it is necessary to [raise an exception](https://docs.python.org/3/tutorial/errors.html#raising-exceptions). When you do this, you should always include a **meaningful error message** to indicate what the source of the error is. This makes your code more readable and helps significantly with debugging. For situations where you know that the error source will be a certain type, you can choose to raise one of the [built in error types](https://docs.python.org/3/library/exceptions.html#base-classes), but should still include a meaningful message.
+
+This particular exercise requires that you use the [raise statement](https://docs.python.org/3/reference/simple_stmts.html#the-raise-statement) to "throw" a `ValueError` when the strands being checked are not the same length. The tests will only pass if you both `raise` the `exception` and include a message with it.
+
+To raise a `ValueError` with a message, write the message as an argument to the `exception` type:
+
+```python
+# When the sequences being passed are not the same length.
+raise ValueError("Strands must be of equal length.")
+```

exercises/practice/hamming/.meta/example.py

@@ -1,5 +1,5 @@
 def distance(s1, s2):
     if len(s1) != len(s2):
-        raise ValueError("Sequences not of equal length.")
+        raise ValueError("Strands must be of equal length.")
 
     return sum(a != b for a, b in zip(s1, s2))

exercises/practice/hamming/.meta/template.j2

@@ -12,14 +12,14 @@ class {{ exercise | camel_case }}Test(unittest.TestCase):
     {% for case in cases -%}
     def test_{{ case["description"] | to_snake }}(self):
         {%- if case is error_case %}
-        with self.assertRaisesWithMessage(ValueError):
+        with self.assertRaises(ValueError) as err:
             {{- test_call(case) }}
+        self.assertEqual(type(err.exception), ValueError)
+        self.assertEqual(err.exception.args[0], "Strands must be of equal length.")
         {%- else %}
         self.assertEqual(
             {{- test_call(case) }},
             {{ case["expected"] }}
         )
         {%- endif %}
     {% endfor %}
-
-{{ macros.footer() }}

exercises/practice/hamming/hamming_test.py

@@ -24,25 +24,29 @@ def test_long_different_strands(self):
         self.assertEqual(distance("GGACGGATTCTG", "AGGACGGATTCT"), 9)
 
     def test_disallow_first_strand_longer(self):
-        with self.assertRaisesWithMessage(ValueError):
+        with self.assertRaises(ValueError) as err:
             distance("AATG", "AAA")
 
+        self.assertEqual(type(err.exception), ValueError)
+        self.assertEqual(err.exception.args[0], "Strands must be of equal length.")
+
     def test_disallow_second_strand_longer(self):
-        with self.assertRaisesWithMessage(ValueError):
+        with self.assertRaises(ValueError) as err:
             distance("ATA", "AGTG")
 
+        self.assertEqual(type(err.exception), ValueError)
+        self.assertEqual(err.exception.args[0], "Strands must be of equal length.")
+
     def test_disallow_left_empty_strand(self):
-        with self.assertRaisesWithMessage(ValueError):
+        with self.assertRaises(ValueError) as err:
             distance("", "G")
 
+        self.assertEqual(type(err.exception), ValueError)
+        self.assertEqual(err.exception.args[0], "Strands must be of equal length.")
+
     def test_disallow_right_empty_strand(self):
-        with self.assertRaisesWithMessage(ValueError):
+        with self.assertRaises(ValueError) as err:
             distance("G", "")
 
-    # Utility functions
-    def assertRaisesWithMessage(self, exception):
-        return self.assertRaisesRegex(exception, r".+")
-
-
-if __name__ == "__main__":
-    unittest.main()
+        self.assertEqual(type(err.exception), ValueError)
+        self.assertEqual(err.exception.args[0], "Strands must be of equal length.")