add before and after hooks

Add hooks that are called before and after the take_action() method of
the command.

Change-Id: Id6527dfe0946c0ab169fc165b84d40f3ff95e08c
Signed-off-by: Doug Hellmann <doug@doughellmann.com>

cliff/command.py

@@ -133,7 +133,12 @@ class Command(object):
 
         Return the value returned by :meth:`take_action` or 0.
         """
-        return self.take_action(parsed_args) or 0
+        for hook in self._hooks:
+            hook.obj.before(parsed_args)
+        return_code = self.take_action(parsed_args) or 0
+        for hook in self._hooks:
+            hook.obj.after(parsed_args, return_code)
+        return return_code
 
 
 class _SmartHelpFormatter(_argparse.HelpFormatter):

cliff/hooks.py

@@ -41,3 +41,25 @@ class CommandHook(object):
     def get_epilog(self):
         "Return text to add to the command help epilog."
         return ''
+
+    @abc.abstractmethod
+    def before(self, parsed_args):
+        """Called before the command's take_action() method.
+
+        Any return value is ignored.
+
+        :param parsed_args: The arguments to the command.
+        :paramtype parsed_args: argparse.Namespace
+        """
+
+    @abc.abstractmethod
+    def after(self, parsed_args, return_code):
+        """Called after the command's take_action() method.
+
+        Any return value is ignored.
+
+        :param parsed_args: The arguments to the command.
+        :paramtype parsed_args: argparse.Namespace
+        :param return_code: The value returned from take_action().
+        :paramtype return_code: int
+        """

cliff/tests/test_command_hooks.py

@@ -62,6 +62,9 @@ class TestCommand(command.Command):
 
 class TestHook(hooks.CommandHook):
 
+    _before_called = False
+    _after_called = False
+
     def get_parser(self, parser):
         parser.add_argument('--added-by-hook')
         return parser
@@ -69,6 +72,12 @@ class TestHook(hooks.CommandHook):
     def get_epilog(self):
         return 'hook epilog'
 
+    def before(self, parsed_args):
+        self._before_called = True
+
+    def after(self, parsed_args, return_code):
+        self._after_called = True
+
 
 class TestCommandLoadHooks(base.TestBase):
 
@@ -112,3 +121,13 @@ class TestHooks(base.TestBase):
     def test_get_epilog(self):
         results = self.cmd.get_epilog()
         self.assertIn('hook epilog', results)
+
+    def test_before(self):
+        self.assertFalse(self.hook._before_called)
+        self.cmd.run(None)
+        self.assertTrue(self.hook._before_called)
+
+    def test_after(self):
+        self.assertFalse(self.hook._after_called)
+        self.cmd.run(None)
+        self.assertTrue(self.hook._after_called)

demoapp/cliffdemo/hook.py

@@ -24,7 +24,7 @@ class Hooked(Command):
     log = logging.getLogger(__name__)
 
     def take_action(self, parsed_args):
-        self.app.stdout.write('this command has an extension')
+        self.app.stdout.write('this command has an extension\n')
 
 
 class Hook(CommandHook):
@@ -42,3 +42,9 @@ class Hook(CommandHook):
 
     def get_epilog(self):
         return 'extension epilog text'
+
+    def before(self, parsed_args):
+        self.cmd.app.stdout.write('before\n')
+
+    def after(self, parsed_args, return_code):
+        self.cmd.app.stdout.write('after\n')

doc/source/user/demoapp.rst

@@ -295,6 +295,12 @@ single ``--added-by-hook`` option.
 
     extension epilog text
 
+    (.venv)$ cliffdemo hooked
+    sample hook get_parser()
+    before
+    this command has an extension
+    after
+
 .. seealso::
 
    :class:`cliff.hooks.CommandHook` -- The API for command hooks.