new method to import downloaders

gallery_dl/downloader/__init__.py

@@ -1 +1,27 @@
+# -*- coding: utf-8 -*-
 
+# Copyright 2015 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 importlib
+
+def find(scheme):
+    """Return downloader class suitable for handling the given scheme"""
+    try:
+        return _cache[scheme]
+    except KeyError:
+        try:
+            module = importlib.import_module("."+scheme, __package__)
+            klass = getattr(module, "Downloader")
+            _cache[scheme] = klass
+            return klass
+        except ImportError:
+            return None
+
+# --------------------------------------------------------------------
+# internals
+
+_cache = {}