diff --git a/DFReader.py b/DFReader.py
index 5b629276d..b25c1089d 100644
--- a/DFReader.py
+++ b/DFReader.py
@@ -560,15 +560,15 @@ class DFMetaData(object):
     def __init__(self, parent):
         self.parent = parent
         self.data = None
-        self.tried = False
+        self.metadata_load_attempted = False
 
     def reset(self):
         '''clear cached data'''
         self.data = None
-        self.tried = False
+        self.metadata_load_attempted = False
 
     # Copy of function in mp_util, to avoid dependency on MavProxy
-    def dot_mavproxy(self,name=None):
+    def dot_mavproxy(self, name=None):
         '''return a path to store mavproxy data'''
         if 'HOME' not in os.environ:
             dir = os.path.join(os.environ['LOCALAPPDATA'], '.mavproxy')
@@ -578,34 +578,33 @@ def dot_mavproxy(self,name=None):
             return dir
         return os.path.join(dir, name)
 
-    def metadata_tree(self,verbose=False):
-        '''return a map between a log message and its metadata. May return None if data is not available'''
+    def metadata_tree(self, verbose=False):
+        ''' return a map between a log message and its metadata. May return
+        None if data is not available '''
         # If we've already tried loading data, use it if we have it
         # This avoid repeated attempts, when the file is not there
         if self.metadata_load_attempted:
             return self.data
-        self.tried = True
+        self.metadata_load_attempted = True
         # Get file name, based on vehicle type
-        mapping = { mavutil.mavlink.MAV_TYPE_GROUND_ROVER : "Rover",
-                    mavutil.mavlink.MAV_TYPE_FIXED_WING : "Plane",
-                    mavutil.mavlink.MAV_TYPE_QUADROTOR : "Copter",
-                    mavutil.mavlink.MAV_TYPE_HELICOPTER : "Copter",
-                    mavutil.mavlink.MAV_TYPE_ANTENNA_TRACKER : "Tracker",
-                    mavutil.mavlink.MAV_TYPE_SUBMARINE : "Sub",
-                    mavutil.mavlink.MAV_TYPE_AIRSHIP : "Blimp",
-                    }
+        mapping = {mavutil.mavlink.MAV_TYPE_GROUND_ROVER : "Rover",
+                   mavutil.mavlink.MAV_TYPE_FIXED_WING : "Plane",
+                   mavutil.mavlink.MAV_TYPE_QUADROTOR : "Copter",
+                   mavutil.mavlink.MAV_TYPE_HELICOPTER : "Copter",
+                   mavutil.mavlink.MAV_TYPE_ANTENNA_TRACKER : "Tracker",
+                   mavutil.mavlink.MAV_TYPE_SUBMARINE : "Sub",
+                   mavutil.mavlink.MAV_TYPE_AIRSHIP : "Blimp",
+                   }
         if self.parent.mav_type not in mapping:
             return None
-            path = self.dot_mavproxy(os.path.join("LogMessages","%s.xml" % mapping[self.parent.mav_type]))
-        else:
-            return None
+        path = self.dot_mavproxy(os.path.join("LogMessages", "%s.xml" % mapping[self.parent.mav_type]))
         # Does the file exist?
         if not os.path.exists(path):
             if verbose:
                 print("Can't find '%s'\nPlease run 'logmessage download' first" % path)
             return None
         # Read in the XML
-        xml = open(path,'rb').read()
+        xml = open(path, 'rb').read()
         from lxml import objectify
         objectify.enable_recursive_str()
         tree = objectify.fromstring(xml)
@@ -617,33 +616,36 @@ def metadata_tree(self,verbose=False):
         self.data = data
         return self.data
 
-    def print_help(self,msg):
+    def print_help(self, msg):
         '''print help for a log message'''
         data = self.metadata_tree(verbose=True)
-        if data is None or msg not in data:
+        if data is None:
+            return
+        if msg not in data:
+            print("No help found for message: %s" % msg)
             return
         node = data[msg]
         # Message name and description
-        print("Log Message: %s\n%s\n" % (msg,node.description.text))
+        print("Log Message: %s\n%s\n" % (msg, node.description.text))
         # Protect against replay messages which dont list their fields
-        if not hasattr(node.fields,'field'):
+        if not hasattr(node.fields, 'field'):
             return
-            # Loop through fields
-            for f in node.fields.field:
-                units = f.get('units')
-                dtype = f.get('type')
-                addstr = ''
-                if units:
-                    addstr = "[%s] " % units
-                elif 'char' in dtype:
-                    addstr = "[%s] " % dtype
-                elif hasattr(f,'enum'):
-                    addstr = "[enum] "
-                elif hasattr(f,'bitmask'):
-                    addstr = "[bitmask] "
-                print("%s %s: %s" % (f.get('name'),addstr,f.description.text))
-
-    def get_description(self,msg):
+        # Loop through fields
+        for f in node.fields.field:
+            units = f.get('units')
+            dtype = f.get('type')
+            addstr = ''
+            if units:
+                addstr = "[%s] " % units
+            elif 'char' in dtype:
+                addstr = "[%s] " % dtype
+            elif hasattr(f, 'enum'):
+                addstr = "[enum] "
+            elif hasattr(f, 'bitmask'):
+                addstr = "[bitmask] "
+            print("%s %s: %s" % (f.get('name'), addstr, f.description.text))
+
+    def get_description(self, msg):
         '''get the description of a log message'''
         data = self.metadata_tree()
         if data is None: