Improve error messages when nargs=0 is supplied to _StoreAction or _AppendAction.

1 files changed, 6 insertions, 2 deletions

diff --git a/argparse.py b/argparse.py
index 89d6f49..1996f46 100644
--- a/argparse.py
+++ b/argparse.py
@@ -787,7 +787,9 @@ class _StoreAction(Action):
                  help=None,
                  metavar=None):
         if nargs == 0:
-            raise ValueError('nargs must be > 0')
+            raise ValueError('nargs for store actions must be > 0; if you '
+                             'have nothing to store, actions such as store '
+                             'true or store const may be more appropriate')
         if const is not None and nargs != OPTIONAL:
             raise ValueError('nargs must be %r to supply const' % OPTIONAL)
         super(_StoreAction, self).__init__(
@@ -877,7 +879,9 @@ class _AppendAction(Action):
                  help=None,
                  metavar=None):
         if nargs == 0:
-            raise ValueError('nargs must be > 0')
+            raise ValueError('nargs for append actions must be > 0; if arg '
+                             'strings are not supplying the value to append, '
+                             'the append const action may be more appropriate')
         if const is not None and nargs != OPTIONAL:
             raise ValueError('nargs must be %r to supply const' % OPTIONAL)
         super(_AppendAction, self).__init__(