Logger messages (#818)

* Change the way logger messages are generated by using the printf-like method
* Use single quotes around log values that can be empty strings
* Fix bug in log message

nw/core/document.py

@@ -73,7 +73,7 @@ class NWDoc():
             return None
 
         docFile = self._docHandle+".nwd"
-        logger.debug("Opening document %s" % docFile)
+        logger.debug("Opening document: %s", docFile)
 
         docPath = os.path.join(self.theProject.projContent, docFile)
         self._fileLoc = docPath
@@ -120,7 +120,7 @@ class NWDoc():
         self.theProject.ensureFolderStructure()
 
         docFile = self._docHandle+".nwd"
-        logger.debug("Saving document %s" % docFile)
+        logger.debug("Saving document: %s", docFile)
 
         docPath = os.path.join(self.theProject.projContent, docFile)
         docTemp = os.path.join(self.theProject.projContent, docFile+"~")
@@ -170,7 +170,7 @@ class NWDoc():
             if os.path.isfile(chkFile):
                 try:
                     os.unlink(chkFile)
-                    logger.debug("Deleted: %s" % chkFile)
+                    logger.debug("Deleted: %s", chkFile)
                 except Exception as e:
                     self._docError = str(e)
                     return False
@@ -237,7 +237,7 @@ class NWDoc():
                     self._docMeta["layout"] = nwItemLayout[metaBits[1]]
 
         else:
-            logger.debug("Ignoring meta data: '%s'" % metaLine.strip())
+            logger.debug("Ignoring meta data: '%s'", metaLine.strip())
 
         return