add a __main__.py file

gallery_dl/__main__.py

@@ -0,0 +1,20 @@
+#!/usr/bin/env python3
+# -*- coding: utf-8 -*-
+
+# Copyright 2017 Mike Fährmann
+#
+# This program is free software; you can redistribute it and/or modify
+# it under the terms of the GNU General Public License version 2 as
+# published by the Free Software Foundation.
+
+import sys
+
+if __package__ is None and not hasattr(sys, "frozen"):
+    import os.path
+    path = os.path.dirname(os.path.dirname(os.path.abspath(__file__)))
+    sys.path.insert(0, os.path.realpath(path))
+
+import gallery_dl
+
+if __name__ == "__main__":
+    gallery_dl.main()