Use power of LazyInitialise to replace ObserverMixin.__init__()

lib/tfw/components/directory_monitor.py

@@ -16,7 +16,6 @@ LOG = logging.getLogger(__name__)
 
 class DirectoryMonitor(ObserverMixin):
     def __init__(self, directories):
-        ObserverMixin.__init__(self)
         self.eventhandler = IdeReloadWatchdogEventHandler()
         for directory in directories:
             self.observer.schedule(self.eventhandler, directory, recursive=True)

lib/tfw/components/history_monitor.py

@@ -37,7 +37,6 @@ class HistoryMonitor(CallbackMixin, ObserverMixin, ABC):
     """
     def __init__(self, histfile):
         CallbackMixin.__init__(self)
-        ObserverMixin.__init__(self)
         self.histfile = histfile
         self._history = []
         self._last_length = len(self._history)

lib/tfw/components/log_monitor.py

@@ -14,7 +14,6 @@ from tfw.mixins import ObserverMixin, SupervisorLogMixin
 class LogMonitor(ObserverMixin):
     def __init__(self, process_name, log_tail=0):
         self.prevent_log_recursion()
-        ObserverMixin.__init__(self)
         event_handler = SendLogWatchdogEventHandler(process_name, log_tail=log_tail)
         self.observer.schedule(
             event_handler,

lib/tfw/mixins/observer_mixin.py

@@ -3,10 +3,13 @@
 
 from watchdog.observers import Observer
 
+from tfw.decorators import LazyInitialise
+
 
 class ObserverMixin:
-    def __init__(self):
-        self.observer = Observer()
+    @LazyInitialise
+    def observer(self):
+        return Observer()
 
     def watch(self):
         self.observer.start()