error-handling: implement exercise

config.json

@@ -1089,6 +1089,16 @@
             "trees"
         ]
     },
+    {
+      "uuid": "3a2a947a-01b3-1e80-e32b-de1756fd88365adf12e",
+      "slug": "error-handling",
+      "core": false,
+      "unlocked_by": null,
+      "difficulty": 3,
+      "topics": [
+        "exception_handling"
+      ]
+    },
     {
       "uuid": "e7351e8e-d3ff-4621-b818-cd55cf05bffd",
       "slug": "accumulate",

exercises/error-handling/README.md

@@ -0,0 +1,23 @@
+# Error Handling
+
+Implement various kinds of error handling and resource management.
+
+An important point of programming is how to handle errors and close
+resources even if errors occur.
+
+This exercise requires you to handle various errors. Because error handling
+is rather programming language specific you'll have to refer to the tests
+for your track to see what's exactly required.
+
+### Submitting Exercises
+
+Note that, when trying to submit an exercise, make sure the solution is in the `exercism/python/<exerciseName>` directory.
+
+For example, if you're submitting `bob.py` for the Bob exercise, the submit command would be something like `exercism submit <path_to_exercism_dir>/python/bob/bob.py`.
+
+
+For more detailed information about running tests, code style and linting,
+please see the [help page](http://exercism.io/languages/python).
+
+## Submitting Incomplete Solutions
+It's possible to submit an incomplete solution so you can see how others have completed the exercise.

exercises/error-handling/error_handling.py

@@ -0,0 +1,14 @@
+def handle_error_by_throwing_exception():
+    pass
+
+
+def handle_error_by_returning_none(input_data):
+    pass
+
+
+def handle_error_by_returning_tuple(input_data):
+    pass
+
+
+def filelike_objects_are_closed_on_exception(filelike_object):
+    pass

exercises/error-handling/error_handling_test.py

@@ -0,0 +1,66 @@
+import unittest
+
+import error_handling as er
+
+
+class FileLike(object):
+    def __init__(self):
+        self.is_open = False
+        self.was_open = False
+        self.did_something = False
+
+    def open(self):
+        self.was_open = False
+        self.is_open = True
+
+    def close(self):
+        self.is_open = False
+        self.was_open = True
+
+    def __enter__(self):
+        self.open()
+        return self
+
+    def __exit__(self, *args):
+        self.close()
+
+    def do_something(self):
+        self.did_something = True
+        raise Exception()
+
+
+class ErrorHandlingTest(unittest.TestCase):
+    def test_throw_exception(self):
+        with self.assertRaises(Exception):
+            er.handle_error_by_throwing_exception()
+
+    def test_return_none(self):
+        self.assertEqual(er.handle_error_by_returning_none('1'), 1,
+                         'Result of valid input should not be None')
+        self.assertIsNone(er.handle_error_by_returning_none('a'),
+                          'Result of invalid input should be None')
+
+    def test_return_tuple(self):
+        successful_result, result = er.handle_error_by_returning_tuple('1')
+        self.assertIs(successful_result, True,
+                      'Valid input should be successful')
+        self.assertEqual(result, 1, 'Result of valid input should not be None')
+
+        failure_result, result = er.handle_error_by_returning_tuple('a')
+        self.assertIs(failure_result, False,
+                      'Invalid input should not be successful')
+
+    def test_filelike_objects_are_closed_on_exception(self):
+        filelike_object = FileLike()
+        with self.assertRaises(Exception):
+            er.filelike_objects_are_closed_on_exception(filelike_object)
+        self.assertIs(filelike_object.is_open, False,
+                      'filelike_object should be closed')
+        self.assertIs(filelike_object.was_open, True,
+                      'filelike_object should have been opened')
+        self.assertIs(filelike_object.did_something, True,
+                      'filelike_object should call do_something()')
+
+
+if __name__ == '__main__':
+    unittest.main()

exercises/error-handling/example.py

@@ -0,0 +1,21 @@
+def handle_error_by_throwing_exception():
+    raise Exception()
+
+
+def handle_error_by_returning_none(input_data):
+    try:
+        return int(input_data)
+    except ValueError:
+        return None
+
+
+def handle_error_by_returning_tuple(input_data):
+    try:
+        return (True, int(input_data))
+    except ValueError:
+        return (False, None)
+
+
+def filelike_objects_are_closed_on_exception(filelike_object):
+    with filelike_object as fobj:
+        fobj.do_something()