From 604857e26e3add54be98545901b289b65cd5de9e Mon Sep 17 00:00:00 2001
From: Kovid Goyal <kovid@kovidgoyal.net>
Date: Wed, 13 Feb 2013 10:47:44 +0530
Subject: [PATCH] ...

---
 src/calibre/ebooks/oeb/polish/container.py | 15 +++++++++++++++
 1 file changed, 15 insertions(+)

diff --git a/src/calibre/ebooks/oeb/polish/container.py b/src/calibre/ebooks/oeb/polish/container.py
index d59071a727..9b84ff82e1 100644
--- a/src/calibre/ebooks/oeb/polish/container.py
+++ b/src/calibre/ebooks/oeb/polish/container.py
@@ -363,7 +363,22 @@ class Container(object):
         self.mime_map[name] = media_type
         return item
 
+    def format_opf(self):
+        mdata = self.opf_xpath('//opf:metadata')[0]
+        mdata.text = '\n    '
+        remove = set()
+        for child in mdata:
+            child.tail = '\n    '
+            if (child.get('name', '').startswith('calibre:') and
+                child.get('content', '').strip() in {'{}', ''}):
+                remove.add(child)
+        for child in remove: mdata.remove(child)
+        if len(mdata) > 0:
+            mdata[-1].tail = '\n  '
+
     def commit_item(self, name):
+        if name == self.opf_name:
+            self.format_opf()
         self.dirtied.remove(name)
         data = self.parsed_cache.pop(name)
         data = serialize(data, self.mime_map[name])