Fix #3022 (Receiving error during convert from pdf to any file)

src/calibre/__init__.py

@@ -114,9 +114,11 @@ def prints(*args, **kwargs):
                     raise
                 arg = repr(arg)
         if not isinstance(arg, str):
+            try:
                 arg = str(arg)
-            if not isinstance(arg, unicode):
-                arg = arg.decode(preferred_encoding, 'replace')
+            except ValueError:
+                arg = unicode(arg)
+            if isinstance(arg, unicode):
                 try:
                     arg = arg.encode(enc)
                 except UnicodeEncodeError:

src/calibre/ebooks/mobi/writer.py

@@ -1972,7 +1972,7 @@ class MobiWriter(object):
                         continue
                     if h not in self._id_offsets:
                         self._oeb.logger.warn('  Ignoring missing TOC entry:',
-                                child)
+                                unicode(child))
                         continue
 
                     currentOffset = self._id_offsets[h]