[modules/memory] Re-enable memory usage module

Add module that shows RAM consumption and opens the gnome-system-monitor
on click.

see #23

bumblebee/modules/memory.py

@@ -0,0 +1,44 @@
+# pylint: disable=C0111,R0903
+
+"""Displays available RAM, total amount of RAM and percentage available.
+
+Parameters:
+    * cpu.warning : Warning threshold in % of memory used (defaults to 80%)
+    * cpu.critical: Critical threshold in % of memory used (defaults to 90%)
+"""
+
+import psutil
+
+import bumblebee.util
+import bumblebee.input
+import bumblebee.output
+import bumblebee.engine
+
+class Module(bumblebee.engine.Module):
+    def __init__(self, engine, config):
+        super(Module, self).__init__(engine, config,
+            bumblebee.output.Widget(full_text=self.memory_usage)
+        )
+        self._mem = psutil.virtual_memory()
+        engine.input.register_callback(self, button=bumblebee.input.LEFT_MOUSE,
+            cmd="gnome-system-monitor")
+
+    def memory_usage(self):
+        used = self._mem.total - self._mem.available
+        return "{}/{} ({:05.02f}%)".format(
+            bumblebee.util.bytefmt(used),
+            bumblebee.util.bytefmt(self._mem.total),
+            self._mem.percent
+        )
+
+    def update(self, widgets):
+        self._mem = psutil.virtual_memory()
+
+    def state(self, widget):
+        if self._mem.percent > float(self.parameter("critical", 90)):
+            return "critical"
+        if self._mem.percent > float(self.parameter("warning", 80)):
+            return "warning"
+        return None
+
+# vim: tabstop=8 expandtab shiftwidth=4 softtabstop=4