inline: allow album field definitions

Under the album_field heading.

beetsplug/inline.py

@@ -46,7 +46,7 @@ def _compile_func(body):
     eval(code, env)
     return env[FUNC_NAME]
 
-def compile_inline(python_code):
+def compile_inline(python_code, album):
     """Given a Python expression or function body, compile it as a path
     field function. The returned function takes a single argument, an
     Item, and returns a Unicode string. If the expression cannot be
@@ -68,10 +68,18 @@ def compile_inline(python_code):
     else:
         is_expr = True
 
+    def _dict_for(obj):
+        if album:
+            out = dict(obj._record)
+            out['items'] = list(obj.items())
+            return out
+        else:
+            return dict(obj.record)
+
     if is_expr:
         # For expressions, just evaluate and return the result.
-        def _expr_func(item):
-            values = dict(item.record)
+        def _expr_func(obj):
+            values = _dict_for(obj)
             try:
                 return eval(code, values)
             except Exception as exc:
@@ -80,8 +88,8 @@ def compile_inline(python_code):
     else:
         # For function bodies, invoke the function with values as global
         # variables.
-        def _func_func(item):
-            func.__globals__.update(item.record)
+        def _func_func(obj):
+            func.__globals__.update(_dict_for(obj))
             try:
                 return func()
             except Exception as exc:
@@ -94,11 +102,18 @@ class InlinePlugin(BeetsPlugin):
 
         config.add({
             'pathfields': {},
+            'album_fields': {},
         })
 
         # Add field expressions.
         for key, view in config['pathfields'].items():
-            log.debug(u'adding template field %s' % key)
-            func = compile_inline(view.get(unicode))
+            log.debug(u'inline: adding item field %s' % key)
+            func = compile_inline(view.get(unicode), False)
             if func is not None:
                 self.template_fields[key] = func
+
+        for key, view in config['album_fields'].items():
+            log.debug(u'inline: adding album field %s' % key)
+            func = compile_inline(view.get(unicode), True)
+            if func is not None:
+                self.album_template_fields[key] = func

docs/changelog.rst

@@ -31,8 +31,9 @@ Changelog
   Thanks to jayme on GitHub.
 * :doc:`/plugins/lyrics`: Lyrics searches should now turn up more results due
   to some fixes in dealing with special characters.
-* Plugins can now provide fields for both Album and Item templates. Thanks
-  to Pedro Silva.
+* Plugins can now provide fields for both Album and Item templates, thanks
+  to Pedro Silva. Accordingly, the :doc:`/plugins/inline` can also now define
+  album fields.
 * The :ref:`fields-cmd` command shows template fields provided by plugins.
   Thanks again to Pedro Silva.
 * Album art filenames now respect the :ref:`replace` configuration.

docs/plugins/inline.rst

@@ -31,6 +31,10 @@ referenced in path templates like so::
     paths:
         default: $initial/$artist/$album%aunique{}/$disc_and_track $title
 
+
+Function Fields
+---------------
+
 If you need to use statements like ``import``, you can write a Python function
 body instead of a single expression. In this case, you'll need to ``return``
 a result for the value of the path field, like so::
@@ -43,3 +47,22 @@ a result for the value of the path field, like so::
 
 You might want to use the YAML syntax for "block literals," in which a leading
 ``|`` character indicates a multi-line block of text.
+
+
+Album Fields
+------------
+
+The above examples define fields for *item* templates, but you can also define
+fields for *album* templates. Use the ``album_fields`` configuration section.
+In this context, all existing album fields are available as variables along
+with ``items``, which is a list of items in the album.
+
+This example defines a ``$bitrate`` field for albums as the average of the
+tracks' fields::
+
+    album_fields:
+        bitrate: |
+            total = 0
+            for item in items:
+                total += item.bitrate
+            return total / len(items)