Ensure --progress goes to stderr

src/alexandria3k/__main__.py

@@ -530,6 +530,9 @@ def get_cli_parser():
         type=str,
         default=[],
         # NOTE: Keep in sync with list in debug.py
+        # Exceptions:
+        # stderr does not work as a Debug API flag (use Debug.set_output)
+        # progress_bar is an undocumented CLI --debug option (use --progress)
         help="""Output debuggging information according to the comma-separated arguments.
     files-read: Counts of Crossref data files read;
     link: Record linking operations;
@@ -591,6 +594,7 @@ def error_raising_main():
         sys.exit(0)
 
     if args.progress:
+        debug.set_output(sys.stderr)
         debug.set_flags(["progress_bar"])
 
     # Handle subcommands

src/alexandria3k/debug.py

@@ -58,6 +58,9 @@ def get_output():
 
 
 # NOTE: Keep in sync with list in __main__.py
+# Exceptions:
+# stderr does not work as a Debug API flag (use Debug.set_output)
+# progress_bar is an undocumented CLI --debug option (use --progress)
 def set_flags(flags):
     """
     Enable the specified debug flags.
@@ -71,7 +74,6 @@ def set_flags(flags):
     * progress: Report population progress;
     * progress_bar: Display a progress bar; (enabled through --progress)
     * sorted-tables: Topologically ordered Crossref query tables;
-    * stderr: Log to standard error;
 
     :param flags: Flags to enable.
     :type flags: list