[modules/sensors] Add support for JSON-formatted sensors output

sensors -j give JSON output, which is much easier to parse than
raw output.

Use this, together with the "path" parameter, to allow robust reading of
sensor values.

fixes #308

bumblebee/modules/sensors.py

@@ -5,12 +5,16 @@
 
 Parameters:
     * sensors.path: path to temperature file (default /sys/class/thermal/thermal_zone0/temp).
+    * sensors.json: if set to "true", interpret sensors.path as JSON "path" in the output
+                    of "sensors -j" (i.e. <key1>/<key2>/.../<value>), for example, path could
+                    be: "coretemp-isa-00000/Core 0/temp1_input" (defaults to "false")
     * sensors.match: (fallback) Line to match against output of 'sensors -u' (default: temp1_input)
     * sensors.match_number: (fallback) which of the matches you want (default -1: last match).
 
 """
 
 import re
+import json
 import logging
 
 import bumblebee.util
@@ -28,11 +32,12 @@ class Module(bumblebee.engine.Module):
         self._mhz = "n/a"
         self._match_number = int(self.parameter("match_number", "-1"))
         self._pattern = re.compile(r"^\s*{}:\s*([\d.]+)$".format(self.parameter("match", "temp1_input")), re.MULTILINE)
+        self._json = bumblebee.util.asbool(self.parameter("json", "false"))
         engine.input.register_callback(self, button=bumblebee.input.LEFT_MOUSE, cmd="xsensors")
         self.determine_method()
 
     def determine_method(self):
-        if self.parameter("path") != None:
+        if self.parameter("path") != None and self._json == False:
             self.use_sensors = False # use thermal zone
         else:
             # try to use output of sensors -u
@@ -45,10 +50,20 @@ class Module(bumblebee.engine.Module):
                 self.use_sensors = False
 
     def _get_temp_from_sensors(self):
-        output = bumblebee.util.execute("sensors -u")
-        match = self._pattern.findall(output)
-        if match:
-            return int(float(match[self._match_number]))
+        if self._json == True:
+            try:
+                output = json.loads(bumblebee.util.execute("sensors -j"))
+                for key in self.parameter("path").split("/"):
+                    output = output[key]
+                return int(float(output))
+            except Exception as e:
+                logging.error("unable to read sensors: {}".format(str(e)))
+                return "unknown"
+        else:
+            output = bumblebee.util.execute("sensors -u")
+            match = self._pattern.findall(output)
+            if match:
+                return int(float(match[self._match_number]))
         return "unknown"
 
     def get_temp(self):