Refactor magic_arguments.py

IPython/core/magic_arguments.py

@@ -173,11 +173,17 b' class magic_arguments(ArgDecorator):'
         return func
 
 
-class argument(ArgDecorator):
-    """ Store arguments and keywords to pass to add_argument().
+class ArgMethodWrapper(ArgDecorator):
 
-    Instances also serve to decorate command methods.
     """
+    Base class to define a wrapper for ArgumentParser method.
+
+    Child class must define either `_method_name` or `add_to_parser`.
+
+    """
+
+    _method_name = None
+
     def __init__(self, *args, **kwds):
         self.args = args
         self.kwds = kwds
@@ -187,36 +193,31 b' class argument(ArgDecorator):'
         """
         if group is not None:
             parser = group
-        parser.add_argument(*self.args, **self.kwds)
+        getattr(parser, self._method_name)(*self.args, **self.kwds)
         return None
 
 
-class defaults(ArgDecorator):
-    """ Store arguments and keywords to pass to set_defaults().
+class argument(ArgMethodWrapper):
+    """ Store arguments and keywords to pass to add_argument().
 
     Instances also serve to decorate command methods.
     """
-    def __init__(self, *args, **kwds):
-        self.args = args
-        self.kwds = kwds
+    _method_name = 'add_argument'
 
-    def add_to_parser(self, parser, group):
-        """ Add this object's information to the parser.
-        """
-        if group is not None:
-            parser = group
-        parser.set_defaults(*self.args, **self.kwds)
-        return None
 
+class defaults(ArgMethodWrapper):
+    """ Store arguments and keywords to pass to set_defaults().
 
-class argument_group(ArgDecorator):
+    Instances also serve to decorate command methods.
+    """
+    _method_name = 'set_defaults'
+
+
+class argument_group(ArgMethodWrapper):
     """ Store arguments and keywords to pass to add_argument_group().
 
     Instances also serve to decorate command methods.
     """
-    def __init__(self, *args, **kwds):
-        self.args = args
-        self.kwds = kwds
 
     def add_to_parser(self, parser, group):
         """ Add this object's information to the parser.