Added exception error message to the output message on failure of multiprocessing.cpu_count().

listdownloader/downloader.py

@@ -171,17 +171,23 @@ def download_files(list_of_urls, to_dir, processes=0):
     list_of_urls = [line.replace(' ', '').replace('\n', '').replace('\t', '') for line in list_of_urls]
     if not os.path.isdir(to_dir):
         mkdir_p(to_dir)
+
+    # try to detect the number of CPUs automatically
     if processes <= 0:
         try:
             processes = mp.cpu_count()
         except NotImplementedError as e:
             sys.stderr.write("Unable to determine the number of CPUs for parallelization. Proceeding sequentially. "
-                             "Consider inputting the number of CPUs manually.\n")
+                             "Consider inputting the number of CPUs manually. The error says: " + str(e) + "\n")
             _download_files(list_of_urls, to_dir)
             return
+
+    # if there's only 1 process or 1 URL, there's no need to use multiprocessing
     elif processes == 1 or len(list_of_urls) == 1:
         _download_files(list_of_urls, to_dir)
         return
+
+    # if number of processes is larger than the number of URLs, reduce the number of processes to save resources
     elif processes > len(list_of_urls):
         processes = len(list_of_urls)
 
@@ -189,4 +195,4 @@ def download_files(list_of_urls, to_dir, processes=0):
     pool = mp.Pool(processes)
     pool.starmap(download_file, params)
     pool.close()
-    pool.join()
+    pool.join()