make date/time tagdisplay convertion only if decimal

cccli/tagdisplay.py

@@ -149,15 +149,21 @@ class TagDisplay(object):
 
     def type_date(self, value):
         '''date type'''
-        d = datetime.datetime.fromtimestamp(float(value))
-        return d.strftime("%d/%m/%Y")
+        if value.isdecimal():
+            d = datetime.datetime.fromtimestamp(float(value))
+            return d.strftime("%d/%m/%Y")
+        return value
 
     def type_time(self, value):
         '''date type'''
-        d = datetime.datetime.fromtimestamp(float(value))
-        return d.strftime("%H:%M:%S")
+        if value.isdecimal():
+            d = datetime.datetime.fromtimestamp(float(value))
+            return d.strftime("%H:%M:%S")
+        return value
 
     def type_datetime(self, value):
         '''date type'''
-        d = datetime.datetime.fromtimestamp(float(value))
-        return d.strftime("%d/%m/%Y %H:%M:%S")
+        if value.isdecimal():
+            d = datetime.datetime.fromtimestamp(float(value))
+            return d.strftime("%d/%m/%Y %H:%M:%S")
+        return value