1) fix problem in rtf metadata writer -- categories isn't a standard option.

2) fix book/base.py to always return a default. That is what python is supposed to do.
3) add ability to code 'key in mi' (the __iter__ function) (base.py)
4) add has_key() to base.py
5) have rename refuse to allow & characters in author names

src/calibre/ebooks/metadata/book/base.py

@@ -133,6 +133,12 @@ class Metadata(object):
             # Don't abuse this privilege
             self.__dict__[field] = val
 
+    def __iter__(self):
+        return object.__getattribute__(self, '_data').iterkeys()
+
+    def has_key(self, key):
+        return key in object.__getattribute__(self, '_data')
+
     def deepcopy(self):
         m = Metadata(None)
         m.__dict__ = copy.deepcopy(self.__dict__)
@@ -140,12 +146,10 @@ class Metadata(object):
         return m
 
     def get(self, field, default=None):
-        if default is not None:
-            try:
-                return self.__getattribute__(field)
-            except AttributeError:
-                return default
-        return self.__getattribute__(field)
+        try:
+            return self.__getattribute__(field)
+        except AttributeError:
+            return default
 
     def get_extra(self, field):
         _data = object.__getattribute__(self, '_data')

src/calibre/ebooks/metadata/rtf.py

@@ -125,7 +125,7 @@ def create_metadata(stream, options):
             au = u', '.join(au)
         author = au.encode('ascii', 'ignore')
         md += r'{\author %s}'%(author,)
-    if options.category:
+    if options.get('category', None):
         category = options.category.encode('ascii', 'ignore')
         md += r'{\category %s}'%(category,)
     comp = options.comment if hasattr(options, 'comment') else options.comments
@@ -180,7 +180,7 @@ def set_metadata(stream, options):
                 src = pat.sub(r'{\\author ' + author + r'}', src)
             else:
                 src = add_metadata_item(src, 'author', author)
-        category = options.category
+        category = options.get('category', None)
         if category != None:
             category = category.encode('ascii', 'replace')
             pat = re.compile(base_pat.replace('name', 'category'), re.DOTALL)

src/calibre/gui2/dialogs/edit_authors_dialog.py

@@ -6,6 +6,7 @@ __license__   = 'GPL v3'
 from PyQt4.Qt import Qt, QDialog, QTableWidgetItem, QAbstractItemView
 
 from calibre.ebooks.metadata import author_to_author_sort
+from calibre.gui2 import error_dialog
 from calibre.gui2.dialogs.edit_authors_dialog_ui import Ui_EditAuthorsDialog
 
 class tableItem(QTableWidgetItem):
@@ -109,6 +110,12 @@ class EditAuthorsDialog(QDialog, Ui_EditAuthorsDialog):
         if col == 0:
             item = self.table.item(row, 0)
             aut  = unicode(item.text()).strip()
+            amper = aut.find('&')
+            if amper >= 0:
+                error_dialog(self.parent(), _('Invalid author name'),
+                        _('Author names cannot contain & characters.')).exec_()
+                aut = aut.replace('&', '%')
+                self.table.item(row, 0).setText(aut)
             c = self.table.item(row, 1)
             c.setText(author_to_author_sort(aut))
             item = c

src/calibre/gui2/tag_view.py

@@ -505,7 +505,12 @@ class TagsModel(QAbstractItemModel): # {{{
         key = item.parent.category_key
         # make certain we know about the item's category
         if key not in self.db.field_metadata:
-            return
+            return False
+        if key == 'authors':
+            if val.find('&') >= 0:
+                error_dialog(self.tags_view, _('Invalid author name'),
+                        _('Author names cannot contain & characters.')).exec_()
+                return False
         if key == 'search':
             if val in saved_searches().names():
                 error_dialog(self.tags_view, _('Duplicate search name'),