Improve error handling between thumbnaildownload and executable

thumbnaildownload will intercept any unexpected Exception,
log it as Critical, and raise a DownloadException.

Executable commonsdownloader will catch any DownloadException
and raise an error.

commonsdownloader/commonsdownloader.py

@@ -6,7 +6,7 @@
 import os
 import logging
 import argparse
-from thumbnaildownload import download_file
+from thumbnaildownload import download_file, DownloadException
 from itertools import izip_longest
 
 
@@ -76,8 +76,11 @@ def download_files_if_not_in_cache(files_iterator, output_path):
             if is_file_in_cache(file_name, width, local_cache):
                 logging.info('Skipping file %s' % file_name)
                 continue
-            download_file(file_name, output_path, width=width)
-            write_file_to_cache(file_name, width, cache_fh)
+            try:
+                download_file(file_name, output_path, width=width)
+                write_file_to_cache(file_name, width, cache_fh)
+            except DownloadException, e:
+                logging.error("Could not download %s: %s", file_name, e.message)
 
 
 class Folder(argparse.Action):

commonsdownloader/thumbnaildownload.py

@@ -119,7 +119,13 @@ def download_file(image_name, output_path, width=DEFAULT_WIDTH):
         logging.info("Requested width is bigger than source - downloading full size")
         contents, output_file_name = get_full_size_file(image_name)
     output_file_path = os.path.join(output_path, output_file_name)
-    with open(output_file_path, 'wb') as f:
-        logging.debug("Writing as %s" % output_file_path)
-        f.write(contents)
-    return output_file_path
+    try:
+        with open(output_file_path, 'wb') as f:
+            logging.debug("Writing as %s" % output_file_path)
+            f.write(contents)
+        return output_file_path
+    except Exception, e:
+        logging.critical(e.message)
+        msg = 'An unexpected error occured when downloading %s to %s: %s' % \
+              (image_name, output_path, e.message)
+        raise DownloadException(msg)