Added error handling instruction append, added additional test cases, corrected JinJa2 template, and regenerated test cases.

Author: BethanyG

exercises/practice/ocr-numbers/.docs/instructions.append.md

@@ -1,3 +1,17 @@
-# Hints
+# Instructions append
 
-Your converter should validate its input and raise a ValueError with a meaningful message if it receives a string that isn't a valid OCR number.
+## 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 `convert()` function receives a string that isn't a valid OCR number. 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 rows aren't multiples of 4
+raise ValueError("Number of input lines is not a multiple of four")
+
+# when the columns aren't multiples of 3
+raise ValueError("Number of input columns is not a multiple of three")
+```

exercises/practice/ocr-numbers/.meta/example.py

@@ -27,9 +27,12 @@ def convert(input_grid):
 
 
 def convert_one_line(input_grid):
-    if (len(input_grid) != NUM_ROWS or len(input_grid[0]) % NUM_COLS or
-            any(len(r) != len(input_grid[0]) for r in input_grid)):
-        raise ValueError('Wrong grid size.')
+    if len(input_grid) != NUM_ROWS:
+        raise ValueError("Number of input lines is not a multiple of four")
+
+    if len(input_grid[0]) % NUM_COLS:
+        raise ValueError("Number of input columns is not a multiple of three")
+
     numbers = split_ocr(input_grid)
     digits = ''
     for n in numbers:

exercises/practice/ocr-numbers/.meta/template.j2

@@ -6,14 +6,14 @@ class {{ exercise | camel_case }}Test(unittest.TestCase):
     def test_{{ case["description"] | to_snake }}(self):
         {% set candidate = case["input"]["rows"] -%}
         {% set output = case["expected"] -%}
-        {% if output is mapping -%}
-        with self.assertRaisesWithMessage(ValueError):
+        {% if case is error_case -%}
+        with self.assertRaises(ValueError) as err:
             {{ case["property"] | to_snake }}({{ candidate }})
+        self.assertEqual(type(err.exception), ValueError)
+        self.assertEqual(err.exception.args[0], "{{ case["expected"]["error"] }}")
         {% else -%}
         {% set expected = case["expected"] -%}
         self.assertEqual({{ case["property"] | to_snake }}({{ candidate }}), "{{ expected }}")
         {% endif %}
 
     {% endfor %}
-
-{{ macros.footer(True) }}

exercises/practice/ocr-numbers/ocr_numbers.py

@@ -1,2 +1,3 @@
 def convert(input_grid):
     pass
+

exercises/practice/ocr-numbers/ocr_numbers_test.py

@@ -20,14 +20,22 @@ def test_unreadable_but_correctly_sized_inputs_return(self):
     def test_input_with_a_number_of_lines_that_is_not_a_multiple_of_four_raises_an_error(
         self,
     ):
-        with self.assertRaisesWithMessage(ValueError):
+        with self.assertRaises(ValueError) as err:
             convert([" _ ", "| |", "   "])
+        self.assertEqual(type(err.exception), ValueError)
+        self.assertEqual(
+            err.exception.args[0], "Number of input lines is not a multiple of four"
+        )
 
     def test_input_with_a_number_of_columns_that_is_not_a_multiple_of_three_raises_an_error(
         self,
     ):
-        with self.assertRaisesWithMessage(ValueError):
+        with self.assertRaises(ValueError) as err:
             convert(["    ", "   |", "   |", "    "])
+        self.assertEqual(type(err.exception), ValueError)
+        self.assertEqual(
+            err.exception.args[0], "Number of input columns is not a multiple of three"
+        )
 
     def test_recognizes_110101100(self):
         self.assertEqual(
@@ -114,11 +122,3 @@ def test_numbers_separated_by_empty_lines_are_recognized_lines_are_joined_by_com
             ),
             "123,456,789",
         )
-
-    # Utility functions
-    def assertRaisesWithMessage(self, exception):
-        return self.assertRaisesRegex(exception, r".+")
-
-
-if __name__ == "__main__":
-    unittest.main()