[core/errors] Add custom exceptions

Add custom exceptions and add error handling to the engine's module
loading logic. I.e. when a non-existent module is loaded, an exception
is thrown now.

see #23

bumblebee-status

@@ -16,6 +16,10 @@ def main():
     engine.run()
 
 if __name__ == "__main__":
+    try:
         main()
+    except bumblebee.error.BaseError as error:
+        sys.stderr.write("fatal: {}\n".format(error))
+        sys.exit(1)
 
 # vim: tabstop=8 expandtab shiftwidth=4 softtabstop=4

bumblebee/engine.py

@@ -1,6 +1,8 @@
 """Core application engine"""
 
+import time
 import importlib
+import bumblebee.error
 
 class Module(object):
     """Module instance base class
@@ -33,7 +35,10 @@ class Engine(object):
 
     def load_module(self, module_name):
         """Load specified module and return it as object"""
+        try:
             module = importlib.import_module("bumblebee.modules.{}".format(module_name))
+        except ImportError as error:
+            raise bumblebee.error.ModuleLoadError(error)
         return getattr(module, "Module")(self)
 
     def running(self):
@@ -53,6 +58,7 @@ class Engine(object):
                 widgets += module.widgets()
             self._output.draw(widgets)
             self._output.flush()
+            time.sleep(1)
 
         self._output.stop()
 

bumblebee/error.py

@@ -0,0 +1,11 @@
+"""Collection of all exceptions raised by this tool"""
+
+class BaseError(Exception):
+    """Base class for all exceptions generated by this tool"""
+    pass
+
+class ModuleLoadError(BaseError):
+    """Raised whenever loading a module fails"""
+    pass
+
+# vim: tabstop=8 expandtab shiftwidth=4 softtabstop=4

tests/test_engine.py

@@ -1,6 +1,7 @@
 # pylint: disable=C0103,C0111
 import unittest
 
+from bumblebee.error import ModuleLoadError
 from bumblebee.engine import Engine
 from bumblebee.config import Config
 
@@ -8,6 +9,7 @@ class TestEngine(unittest.TestCase):
     def setUp(self):
         self.engine = Engine(Config())
         self.testModule = "test"
+        self.invalidModule = "no-such-module"
         self.testModuleSpec = "bumblebee.modules.{}".format(self.testModule)
         self.testModules = [
             {"module": "test", "name": "a"},
@@ -23,6 +25,14 @@ class TestEngine(unittest.TestCase):
         module = self.engine.load_module(self.testModule)
         self.assertEquals(module.__module__, self.testModuleSpec)
 
+    def test_load_invalid_module(self):
+        with self.assertRaises(ModuleLoadError):
+            self.engine.load_module(self.invalidModule)
+
+    def test_load_none(self):
+        with self.assertRaises(ModuleLoadError):
+            self.engine.load_module(None)
+
     def test_load_modules(self):
         modules = self.engine.load_modules(self.testModules)
         self.assertEquals(len(modules), len(self.testModules))