Convert FEED settings from `%s` to `{slug}` redux (#2432)

* Convert FEED settings from `%s` to `{slug}` redux

Closes #2106, Closes #2383

10 files changed, 165 insertions, 102 deletions

diff --git a/THANKS b/THANKS
index cfa343f6..348c0b59 100644
--- a/THANKS
+++ b/THANKS
@@ -155,6 +155,7 @@ Tshepang Lekhonkhobe
 Valentin-Costel Hăloiu
 Vlad Niculae
 William Light
+William Minchin
 Wladislaw Merezhko
 W. Trevor King
 Zoresvit
diff --git a/docs/changelog.rst b/docs/changelog.rst
index 858a6e1b..3d3fddc8 100644
--- a/docs/changelog.rst
+++ b/docs/changelog.rst
@@ -4,6 +4,9 @@ Release history
 Next release
 ============
 
+* All settings for slugs now use ``{slug}`` and/or ``{lang}`` rather than
+  ``%s``. If ``%s``-style settings are encountered, Pelican will emit a warning
+  and fallback to the default setting.
 * New signal: ``feed_generated``
 * Replace Fabric by Invoke and ``fabfile.py`` template by ``tasks.py``.
 * Replace ``SLUG_SUBSTITUTIONS`` (and friends) by ``SLUG_REGEX_SUBSTITUTIONS``
diff --git a/docs/plugins.rst b/docs/plugins.rst
index 4e0ec6d1..18c18364 100644
--- a/docs/plugins.rst
+++ b/docs/plugins.rst
@@ -60,7 +60,7 @@ which you map the signals to your plugin logic. Let's take a simple example::
     from pelican import signals
 
     def test(sender):
-        print "%s initialized !!" % sender
+        print("{} initialized !!".format(sender))
 
     def register():
         signals.initialized.connect(test)
diff --git a/docs/settings.rst b/docs/settings.rst
index 28b68980..7d5fa324 100644
--- a/docs/settings.rst
+++ b/docs/settings.rst
@@ -879,59 +879,61 @@ the ``TAG_FEED_ATOM`` and ``TAG_FEED_RSS`` settings:
    Relative URL of the all-posts RSS feed. If not set, ``FEED_ALL_RSS`` is used
    both for save location and URL.
 
-.. data:: CATEGORY_FEED_ATOM = 'feeds/%s.atom.xml'
+.. data:: CATEGORY_FEED_ATOM = 'feeds/{slug}.atom.xml'
 
    The location to save the category Atom feeds. [2]_
 
 .. data:: CATEGORY_FEED_ATOM_URL = None
 
-   Relative URL of the category Atom feeds, including the ``%s`` placeholder.
-   [2]_ If not set, ``CATEGORY_FEED_ATOM`` is used both for save location and
-   URL.
+   Relative URL of the category Atom feeds, including the ``{slug}``
+   placeholder. [2]_ If not set, ``CATEGORY_FEED_ATOM`` is used both for save
+   location and URL.
 
 .. data:: CATEGORY_FEED_RSS = None, i.e. no RSS
 
-   The location to save the category RSS feeds, including the ``%s``
+   The location to save the category RSS feeds, including the ``{slug}``
    placeholder. [2]_
 
 .. data:: CATEGORY_FEED_RSS_URL = None
 
-   Relative URL of the category RSS feeds, including the ``%s`` placeholder.
-   [2]_ If not set, ``CATEGORY_FEED_RSS`` is used both for save location and
-   URL.
+   Relative URL of the category RSS feeds, including the ``{slug}``
+   placeholder. [2]_ If not set, ``CATEGORY_FEED_RSS`` is used both for save
+   location and URL.
 
-.. data:: AUTHOR_FEED_ATOM = 'feeds/%s.atom.xml'
+.. data:: AUTHOR_FEED_ATOM = 'feeds/{slug}.atom.xml'
 
    The location to save the author Atom feeds. [2]_
 
 .. data:: AUTHOR_FEED_ATOM_URL = None
 
-   Relative URL of the author Atom feeds, including the ``%s`` placeholder.
+   Relative URL of the author Atom feeds, including the ``{slug}`` placeholder.
    [2]_ If not set, ``AUTHOR_FEED_ATOM`` is used both for save location and
    URL.
 
-.. data:: AUTHOR_FEED_RSS = 'feeds/%s.rss.xml'
+.. data:: AUTHOR_FEED_RSS = 'feeds/{slug}.rss.xml'
 
    The location to save the author RSS feeds. [2]_
 
 .. data:: AUTHOR_FEED_RSS_URL = None
 
-   Relative URL of the author RSS feeds, including the ``%s`` placeholder. [2]_
-   If not set, ``AUTHOR_FEED_RSS`` is used both for save location and URL.
+   Relative URL of the author RSS feeds, including the ``{slug}`` placeholder.
+   [2]_ If not set, ``AUTHOR_FEED_RSS`` is used both for save location and URL.
 
 .. data:: TAG_FEED_ATOM = None, i.e. no tag feed
 
-   The location to save the tag Atom feed, including the ``%s`` placeholder.
-   [2]_
+   The location to save the tag Atom feed, including the ``{slug}``
+   placeholder. [2]_
 
 .. data:: TAG_FEED_ATOM_URL = None
 
-   Relative URL of the tag Atom feed, including the ``%s`` placeholder. [2]_
+   Relative URL of the tag Atom feed, including the ``{slug}`` placeholder.
+   [2]_
 
 .. data:: TAG_FEED_RSS = None, i.e. no RSS tag feed
 
-   Relative URL to output the tag RSS feed, including the ``%s`` placeholder.
-   If not set, ``TAG_FEED_RSS`` is used both for save location and URL.
+   Relative URL to output the tag RSS feed, including the ``{slug}``
+   placeholder. If not set, ``TAG_FEED_RSS`` is used both for save location and
+   URL.
 
 .. data:: FEED_MAX_ITEMS
 
@@ -946,7 +948,7 @@ the ``TAG_FEED_ATOM`` and ``TAG_FEED_RSS`` settings:
 
 If you don't want to generate some or any of these feeds, set the above variables to ``None``.
 
-.. [2] ``%s`` is replaced by name of the category / author / tag.
+.. [2] ``{slug}`` is replaced by name of the category / author / tag.
 
 
 FeedBurner
@@ -1050,13 +1052,13 @@ more information.
    of one another. May be a string or a collection of strings. Set to ``None``
    or ``False`` to disable the identification of translations.
 
-.. data:: TRANSLATION_FEED_ATOM = 'feeds/all-%s.atom.xml'
+.. data:: TRANSLATION_FEED_ATOM = 'feeds/all-{lang}.atom.xml'
 
    The location to save the Atom feed for translations. [3]_
 
 .. data:: TRANSLATION_FEED_ATOM_URL = None
 
-   Relative URL of the Atom feed for translations, including the ``%s``
+   Relative URL of the Atom feed for translations, including the ``{lang}``
    placeholder. [3]_ If not set, ``TRANSLATION_FEED_ATOM`` is used both for
    save location and URL.
 
@@ -1066,11 +1068,11 @@ more information.
 
 .. data:: TRANSLATION_FEED_RSS_URL = None
 
-   Relative URL of the RSS feed for translations, including the ``%s``
+   Relative URL of the RSS feed for translations, including the ``{lang}``
    placeholder. [3]_ If not set, ``TRANSLATION_FEED_RSS`` is used both for save
    location and URL.
 
-.. [3] %s is the language
+.. [3] {lang} is the language code
 
 
 Ordering content
diff --git a/pelican/generators.py b/pelican/generators.py
index 90e4c8a5..0e772a62 100644
--- a/pelican/generators.py
+++ b/pelican/generators.py
@@ -302,17 +302,21 @@ class ArticlesGenerator(CachingGenerator):
         """Generate the feeds from the current context, and output files."""
 
         if self.settings.get('FEED_ATOM'):
-            writer.write_feed(self.articles, self.context,
-                              self.settings['FEED_ATOM'],
-                              self.settings.get('FEED_ATOM_URL',
-                                                self.settings['FEED_ATOM']))
+            writer.write_feed(
+                self.articles,
+                self.context,
+                self.settings['FEED_ATOM'],
+                self.settings.get('FEED_ATOM_URL', self.settings['FEED_ATOM'])
+                )
 
         if self.settings.get('FEED_RSS'):
-            writer.write_feed(self.articles, self.context,
-                              self.settings['FEED_RSS'],
-                              self.settings.get('FEED_RSS_URL',
-                                                self.settings['FEED_RSS']),
-                              feed_type='rss')
+            writer.write_feed(
+                self.articles,
+                self.context,
+                self.settings['FEED_RSS'],
+                self.settings.get('FEED_RSS_URL', self.settings['FEED_RSS']),
+                feed_type='rss'
+                )
 
         if (self.settings.get('FEED_ALL_ATOM') or
                 self.settings.get('FEED_ALL_RSS')):
@@ -323,80 +327,105 @@ class ArticlesGenerator(CachingGenerator):
                           order_by=self.settings['ARTICLE_ORDER_BY'])
 
             if self.settings.get('FEED_ALL_ATOM'):
-                writer.write_feed(all_articles, self.context,
-                                  self.settings['FEED_ALL_ATOM'],
-                                  self.settings.get(
-                                      'FEED_ALL_ATOM_URL',
-                                      self.settings['FEED_ALL_ATOM']))
+                writer.write_feed(
+                    all_articles,
+                    self.context,
+                    self.settings['FEED_ALL_ATOM'],
+                    self.settings.get('FEED_ALL_ATOM_URL',
+                                      self.settings['FEED_ALL_ATOM'])
+                    )
 
             if self.settings.get('FEED_ALL_RSS'):
-                writer.write_feed(all_articles, self.context,
-                                  self.settings['FEED_ALL_RSS'],
-                                  self.settings.get(
-                                      'FEED_ALL_RSS_URL',
+                writer.write_feed(
+                    all_articles,
+                    self.context,
+                    self.settings['FEED_ALL_RSS'],
+                    self.settings.get('FEED_ALL_RSS_URL',
                                       self.settings['FEED_ALL_RSS']),
-                                  feed_type='rss')
+                    feed_type='rss'
+                    )
 
         for cat, arts in self.categories:
             if self.settings.get('CATEGORY_FEED_ATOM'):
-                writer.write_feed(arts, self.context,
-                                  self.settings['CATEGORY_FEED_ATOM']
-                                  % cat.slug,
-                                  self.settings.get(
-                                      'CATEGORY_FEED_ATOM_URL',
-                                      self.settings['CATEGORY_FEED_ATOM'])
-                                  % cat.slug, feed_title=cat.name)
+                writer.write_feed(
+                    arts,
+                    self.context,
+                    self.settings['CATEGORY_FEED_ATOM'].format(slug=cat.slug),
+                    self.settings.get(
+                        'CATEGORY_FEED_ATOM_URL',
+                        self.settings['CATEGORY_FEED_ATOM']).format(
+                            slug=cat.slug
+                        ),
+                    feed_title=cat.name
+                    )
 
             if self.settings.get('CATEGORY_FEED_RSS'):
-                writer.write_feed(arts, self.context,
-                                  self.settings['CATEGORY_FEED_RSS']
-                                  % cat.slug,
-                                  self.settings.get(
-                                      'CATEGORY_FEED_RSS_URL',
-                                      self.settings['CATEGORY_FEED_RSS'])
-                                  % cat.slug, feed_title=cat.name,
-                                  feed_type='rss')
+                writer.write_feed(
+                    arts,
+                    self.context,
+                    self.settings['CATEGORY_FEED_RSS'].format(slug=cat.slug),
+                    self.settings.get(
+                        'CATEGORY_FEED_RSS_URL',
+                        self.settings['CATEGORY_FEED_RSS']).format(
+                            slug=cat.slug
+                        ),
+                    feed_title=cat.name,
+                    feed_type='rss'
+                    )
 
         for auth, arts in self.authors:
             if self.settings.get('AUTHOR_FEED_ATOM'):
-                writer.write_feed(arts, self.context,
-                                  self.settings['AUTHOR_FEED_ATOM']
-                                  % auth.slug,
-                                  self.settings.get(
-                                      'AUTHOR_FEED_ATOM_URL',
-                                      self.settings['AUTHOR_FEED_ATOM'])
-                                  % auth.slug, feed_title=auth.name)
+                writer.write_feed(
+                    arts,
+                    self.context,
+                    self.settings['AUTHOR_FEED_ATOM'].format(slug=auth.slug),
+                    self.settings.get(
+                        'AUTHOR_FEED_ATOM_URL',
+                        self.settings['AUTHOR_FEED_ATOM']
+                        ).format(slug=auth.slug),
+                    feed_title=auth.name
+                    )
 
             if self.settings.get('AUTHOR_FEED_RSS'):
-                writer.write_feed(arts, self.context,
-                                  self.settings['AUTHOR_FEED_RSS']
-                                  % auth.slug,
-                                  self.settings.get(
-                                      'AUTHOR_FEED_RSS_URL',
-                                      self.settings['AUTHOR_FEED_RSS'])
-                                  % auth.slug, feed_title=auth.name,
-                                  feed_type='rss')
+                writer.write_feed(
+                    arts,
+                    self.context,
+                    self.settings['AUTHOR_FEED_RSS'].format(slug=auth.slug),
+                    self.settings.get(
+                        'AUTHOR_FEED_RSS_URL',
+                        self.settings['AUTHOR_FEED_RSS']
+                        ).format(slug=auth.slug),
+                    feed_title=auth.name,
+                    feed_type='rss'
+                    )
 
         if (self.settings.get('TAG_FEED_ATOM') or
                 self.settings.get('TAG_FEED_RSS')):
             for tag, arts in self.tags.items():
                 if self.settings.get('TAG_FEED_ATOM'):
-                    writer.write_feed(arts, self.context,
-                                      self.settings['TAG_FEED_ATOM']
-                                      % tag.slug,
-                                      self.settings.get(
-                                          'TAG_FEED_ATOM_URL',
-                                          self.settings['TAG_FEED_ATOM'])
-                                      % tag.slug, feed_title=tag.name)
+                    writer.write_feed(
+                        arts,
+                        self.context,
+                        self.settings['TAG_FEED_ATOM'].format(slug=tag.slug),
+                        self.settings.get(
+                            'TAG_FEED_ATOM_URL',
+                            self.settings['TAG_FEED_ATOM']
+                            ).format(slug=tag.slug),
+                        feed_title=tag.name
+                        )
 
                 if self.settings.get('TAG_FEED_RSS'):
-                    writer.write_feed(arts, self.context,
-                                      self.settings['TAG_FEED_RSS'] % tag.slug,
-                                      self.settings.get(
-                                          'TAG_FEED_RSS_URL',
-                                          self.settings['TAG_FEED_RSS'])
-                                      % tag.slug, feed_title=tag.name,
-                                      feed_type='rss')
+                    writer.write_feed(
+                        arts,
+                        self.context,
+                        self.settings['TAG_FEED_RSS'].format(slug=tag.slug),
+                        self.settings.get(
+                            'TAG_FEED_RSS_URL',
+                            self.settings['TAG_FEED_RSS']
+                            ).format(slug=tag.slug),
+                        feed_title=tag.name,
+                        feed_type='rss'
+                        )
 
         if (self.settings.get('TRANSLATION_FEED_ATOM') or
                 self.settings.get('TRANSLATION_FEED_RSS')):
@@ -409,19 +438,27 @@ class ArticlesGenerator(CachingGenerator):
                     items, order_by=self.settings['ARTICLE_ORDER_BY'])
                 if self.settings.get('TRANSLATION_FEED_ATOM'):
                     writer.write_feed(
-                        items, self.context,
-                        self.settings['TRANSLATION_FEED_ATOM'] % lang,
+                        items,
+                        self.context,
+                        self.settings['TRANSLATION_FEED_ATOM']
+                            .format(lang=lang),
                         self.settings.get(
                             'TRANSLATION_FEED_ATOM_URL',
-                            self.settings['TRANSLATION_FEED_ATOM']) % lang)
+                            self.settings['TRANSLATION_FEED_ATOM']
+                            ).format(lang=lang),
+                        )
                 if self.settings.get('TRANSLATION_FEED_RSS'):
                     writer.write_feed(
-                        items, self.context,
-                        self.settings['TRANSLATION_FEED_RSS'] % lang,
+                        items,
+                        self.context,
+                        self.settings['TRANSLATION_FEED_RSS']
+                            .format(lang=lang),
                         self.settings.get(
                             'TRANSLATION_FEED_RSS_URL',
-                            self.settings['TRANSLATION_FEED_RSS']) % lang,
-                        feed_type='rss')
+                            self.settings['TRANSLATION_FEED_RSS']
+                            ).format(lang=lang),
+                        feed_type='rss'
+                        )
 
     def generate_articles(self, write):
         """Generate the articles."""
diff --git a/pelican/settings.py b/pelican/settings.py
index 0bf4284a..6907051c 100644
--- a/pelican/settings.py
+++ b/pelican/settings.py
@@ -45,10 +45,10 @@ DEFAULT_CONFIG = {
     'THEME_STATIC_DIR': 'theme',
     'THEME_STATIC_PATHS': ['static', ],
     'FEED_ALL_ATOM': posix_join('feeds', 'all.atom.xml'),
-    'CATEGORY_FEED_ATOM': posix_join('feeds', '%s.atom.xml'),
-    'AUTHOR_FEED_ATOM': posix_join('feeds', '%s.atom.xml'),
-    'AUTHOR_FEED_RSS': posix_join('feeds', '%s.rss.xml'),
-    'TRANSLATION_FEED_ATOM': posix_join('feeds', 'all-%s.atom.xml'),
+    'CATEGORY_FEED_ATOM': posix_join('feeds', '{slug}.atom.xml'),
+    'AUTHOR_FEED_ATOM': posix_join('feeds', '{slug}.atom.xml'),
+    'AUTHOR_FEED_RSS': posix_join('feeds', '{slug}.rss.xml'),
+    'TRANSLATION_FEED_ATOM': posix_join('feeds', 'all-{lang}.atom.xml'),
     'FEED_MAX_ITEMS': '',
     'RSS_FEED_SUMMARY_ONLY': True,
     'SITEURL': '',
@@ -385,6 +385,26 @@ def handle_deprecated_settings(settings):
                 settings[f + '_REGEX_SUBSTITUTIONS'] = regex_subs
             settings.pop(f + '_SUBSTITUTIONS', None)
 
+    # `%s` -> '{slug}` or `{lang}` in FEED settings
+        for key in ['TRANSLATION_FEED_ATOM',
+                    'TRANSLATION_FEED_RSS'
+                    ]:
+            if key in settings and '%s' in settings[key]:
+                logger.warning('%%s usage in %s is deprecated, use {lang} '
+                               'instead. Falling back to default.', key)
+                settings[key] = DEFAULT_CONFIG[key]
+        for key in ['AUTHOR_FEED_ATOM',
+                    'AUTHOR_FEED_RSS',
+                    'CATEGORY_FEED_ATOM',
+                    'CATEGORY_FEED_RSS',
+                    'TAG_FEED_ATOM',
+                    'TAG_FEED_RSS',
+                    ]:
+            if key in settings and '%s' in settings[key]:
+                logger.warning('%%s usage in %s is deprecated, use {slug} '
+                               'instead. Falling back to default.', key)
+                settings[key] = DEFAULT_CONFIG[key]
+
     return settings
 
 
diff --git a/pelican/tests/default_conf.py b/pelican/tests/default_conf.py
index 77c2b947..a567dc10 100644
--- a/pelican/tests/default_conf.py
+++ b/pelican/tests/default_conf.py
@@ -12,7 +12,7 @@ REVERSE_CATEGORY_ORDER = True
 DEFAULT_PAGINATION = 2
 
 FEED_RSS = 'feeds/all.rss.xml'
-CATEGORY_FEED_RSS = 'feeds/%s.rss.xml'
+CATEGORY_FEED_RSS = 'feeds/{slug}.rss.xml'
 
 LINKS = (('Biologeek', 'http://biologeek.org'),
          ('Filyb', "http://filyb.info/"),
diff --git a/pelican/tools/templates/publishconf.py.jinja2 b/pelican/tools/templates/publishconf.py.jinja2
index 4b9a7cba..913de7f1 100755
--- a/pelican/tools/templates/publishconf.py.jinja2
+++ b/pelican/tools/templates/publishconf.py.jinja2
@@ -15,7 +15,7 @@ SITEURL = '{{siteurl}}'
 RELATIVE_URLS = False
 
 FEED_ALL_ATOM = 'feeds/all.atom.xml'
-CATEGORY_FEED_ATOM = 'feeds/%s.atom.xml'
+CATEGORY_FEED_ATOM = 'feeds/{slug}.atom.xml'
 
 DELETE_OUTPUT_DIRECTORY = True
 
diff --git a/samples/pelican.conf.py b/samples/pelican.conf.py
index da5c5dc5..0f67ee83 100755
--- a/samples/pelican.conf.py
+++ b/samples/pelican.conf.py
@@ -18,7 +18,7 @@ DEFAULT_PAGINATION = 4
 DEFAULT_DATE = (2012, 3, 2, 14, 1, 1)
 
 FEED_ALL_RSS = 'feeds/all.rss.xml'
-CATEGORY_FEED_RSS = 'feeds/%s.rss.xml'
+CATEGORY_FEED_RSS = 'feeds/{slug}.rss.xml'
 
 LINKS = (('Biologeek', 'http://biologeek.org'),
          ('Filyb', "http://filyb.info/"),
diff --git a/samples/pelican.conf_FR.py b/samples/pelican.conf_FR.py
index 54b348c4..b1571e8a 100644
--- a/samples/pelican.conf_FR.py
+++ b/samples/pelican.conf_FR.py
@@ -22,7 +22,7 @@ ARTICLE_URL = 'posts/{date:%Y}/{date:%B}/{date:%d}/{slug}/'
 ARTICLE_SAVE_AS = ARTICLE_URL + 'index.html'
 
 FEED_ALL_RSS = 'feeds/all.rss.xml'
-CATEGORY_FEED_RSS = 'feeds/%s.rss.xml'
+CATEGORY_FEED_RSS = 'feeds/{slug}.rss.xml'
 
 LINKS = (('Biologeek', 'http://biologeek.org'),
          ('Filyb', "http://filyb.info/"),