Move screen stop/start logic into context manager.

As well as reducing duplication and adding screen size detection to
:pipeto and :pyshell, this ensures that the screen is always restarted,
resulting in cleaner error handling if an error occurs while the screen
is stopped.

alot/commands/globals.py

@@ -284,13 +284,8 @@ def thread_code(*_):
             d = threads.deferToThread(thread_code)
             d.addCallback(afterwards)
         else:
-            ui.mainloop.stop()
-            ret = thread_code()
-            ui.mainloop.start()
-
-            # make sure urwid renders its canvas at the correct size
-            ui.mainloop.screen_size = None
-            ui.mainloop.draw_screen()
+            with ui.paused():
+                ret = thread_code()
 
             afterwards(ret)
 
@@ -348,9 +343,8 @@ class PythonShellCommand(Command):
     repeatable = True
 
     def apply(self, ui):
-        ui.mainloop.stop()
-        code.interact(local=locals())
-        ui.mainloop.start()
+        with ui.paused():
+            code.interact(local=locals())
 
 
 @registerCommand(MODE, 'repeat')

alot/commands/thread.py

@@ -769,18 +769,15 @@ def apply(self, ui):
                 if self.notify_stdout:
                     ui.notify(out)
             else:
-                logging.debug('stop urwid mainloop')
-                ui.mainloop.stop()
-                logging.debug('call: %s', self.cmd)
-                # if proc.stdout is defined later calls to communicate
-                # seem to be non-blocking!
-                proc = subprocess.Popen(self.cmd, shell=True,
-                                        stdin=subprocess.PIPE,
-                                        # stdout=subprocess.PIPE,
-                                        stderr=subprocess.PIPE)
-                out, err = proc.communicate(mail)
-                logging.debug('start urwid mainloop')
-                ui.mainloop.start()
+                with ui.paused():
+                    logging.debug('call: %s', self.cmd)
+                    # if proc.stdout is defined later calls to communicate
+                    # seem to be non-blocking!
+                    proc = subprocess.Popen(self.cmd, shell=True,
+                                            stdin=subprocess.PIPE,
+                                            # stdout=subprocess.PIPE,
+                                            stderr=subprocess.PIPE)
+                    out, err = proc.communicate(mail)
             if err:
                 ui.notify(err, priority='error')
                 return

alot/ui.py

@@ -7,6 +7,7 @@
 import os
 import signal
 import codecs
+import contextlib
 
 from twisted.internet import reactor, defer, task
 import urwid
@@ -363,6 +364,24 @@ def exit():
             exit_msg = 'Could not stop reactor: {}.'.format(e)
             logging.error('%s\nShutting down anyway..', exit_msg)
 
+    @contextlib.contextmanager
+    def paused(self):
+        """
+        context manager that pauses the UI to allow running external commands.
+
+        If an exception occurs, the UI will be started before the exception is
+        re-raised.
+        """
+        self.mainloop.stop()
+        try:
+            yield
+        finally:
+            self.mainloop.start()
+
+            # make sure urwid renders its canvas at the correct size
+            self.mainloop.screen_size = None
+            self.mainloop.draw_screen()
+
     def buffer_open(self, buf):
         """register and focus new :class:`~alot.buffers.Buffer`."""
 

tests/utilities.py

@@ -175,6 +175,7 @@ def make_key(revoked=False, expired=False, invalid=False, can_encrypt=True,
 
 def make_ui(**kwargs):
     ui = mock.Mock(**kwargs)
+    ui.paused.return_value = mock.MagicMock()
 
     return ui