contents: Add rich comparisons to URLWrapper for easy sorting

There have been earlier attempts to sort categories and authors
[1,2,3], but they either sorted based on the object id [3], or only
sorted the main author and categories list.

This patch uses rich comparisons (keyed off URLWrapper.name, but
easily adjustable in subclasses) to make the objects sortable without
specifying a key for each sort.  For example, now

  {% for tag, articles in tags|sort %}

works as expected in a Jinja template.

The functools.total_ordering decorator fills in the missing rich
comparisons [4,5].

[1]: 877d454c8f
[2]: 7f36e0ed20
[3]: d0ec18f4db
[4]: http://docs.python.org/2/library/functools.html#functools.total_ordering
[5]: http://docs.python.org/3/library/functools.html#functools.total_ordering

pelican/contents.py

@@ -243,7 +243,9 @@ class Article(Page):
 class Quote(Page):
     base_properties = ('author', 'date')
 
+
 @python_2_unicode_compatible
+@functools.total_ordering
 class URLWrapper(object):
     def __init__(self, name, settings):
         self.name = name
@@ -256,8 +258,20 @@ class URLWrapper(object):
     def __hash__(self):
         return hash(self.name)
 
+    def _key(self):
+        return self.name
+
+    def _normalize_key(self, key):
+        return six.text_type(key)
+
     def __eq__(self, other):
-        return self.name == other
+        return self._key() == self._normalize_key(other)
+
+    def __ne__(self, other):
+        return self._key() != self._normalize_key(other)
+
+    def __lt__(self, other):
+        return self._key() < self._normalize_key(other)
 
     def __str__(self):
         return self.name

pelican/generators.py

@@ -416,11 +416,10 @@ class ArticlesGenerator(Generator):
         # order the categories per name
         self.categories = list(self.categories.items())
         self.categories.sort(
-                key=lambda item: item[0].name,
                 reverse=self.settings['REVERSE_CATEGORY_ORDER'])
 
         self.authors = list(self.authors.items())
-        self.authors.sort(key=lambda item: item[0].name)
+        self.authors.sort()
 
         self._update_context(('articles', 'dates', 'tags', 'categories',
                               'tag_cloud', 'authors', 'related_posts'))