enable writing of only selected output paths

- add WRITE_SELECTED setting
- add --write-selected commandline option

pelican/utils.py

@@ -658,3 +658,17 @@ class FileStampDataCacher(FileDataCacher):
         if stamp != self._get_file_stamp(filename):
             return default
         return data
+
+
+def is_selected_for_writing(settings, path):
+    '''Check whether path is selected for writing
+    according to the WRITE_SELECTED list
+
+    If WRITE_SELECTED is an empty list (default),
+    any path is selected for writing.
+    '''
+    if settings['WRITE_SELECTED']:
+        return path in settings['WRITE_SELECTED']
+    else:
+        return True
+