Better error messages for errors like type='int'. This actually caught a bug in one of the tests and as I result, this patch also makes sure that types display as their type name when %(type)s is specified.

3 files changed, 14 insertions, 1 deletions

diff --git a/NEWS.txt b/NEWS.txt
index 98c7139..b13da28 100644
--- a/NEWS.txt
+++ b/NEWS.txt
@@ -9,6 +9,7 @@ What's New in argparse 1.1
 - Issue #39: Better error messages for invalid actions.
 - Issue #43: Deprecate ArgumentParser(..., version=XXX, ...) and friends.
 - Issue #46: Allow single character options, e.g. '-' and '+'.
+- Issue #51: Better error messages for errors like type='int'.
 - Namespace objects now support "in" (i.e. __contains__).
 - Usage and help (but not version) messages are written to stdout, not stderr.
 
diff --git a/argparse.py b/argparse.py
index c89618b..4966b14 100644
--- a/argparse.py
+++ b/argparse.py
@@ -621,6 +621,9 @@ class HelpFormatter(object):
         for name in list(params):
             if params[name] is SUPPRESS:
                 del params[name]
+        for name in list(params):
+            if hasattr(params[name], '__name__'):
+                params[name] = params[name].__name__
         if params.get('choices') is not None:
             choices_str = ', '.join([str(c) for c in params['choices']])
             params['choices'] = choices_str
@@ -1297,6 +1300,12 @@ class _ActionsContainer(object):
         if not _callable(action_class):
             raise ValueError('unknown action "%s"' % action_class)
         action = action_class(**kwargs)
+
+        # raise an error if the action type is not callable
+        type_func = self._registry_get('type', action.type, action.type)
+        if not _callable(type_func):
+            raise ValueError('%r is not callable' % type_func)
+
         return self._add_action(action)
 
     def add_argument_group(self, *args, **kwargs):
diff --git a/test/test_argparse.py b/test/test_argparse.py
index 968843c..4392e42 100644
--- a/test/test_argparse.py
+++ b/test/test_argparse.py
@@ -3300,7 +3300,7 @@ class TestHelpVariableExpansion(HelpTestCase):
 
     parser_signature = Sig(prog='PROG')
     argument_signatures = [
-        Sig('-x', type='int',
+        Sig('-x', type=int,
             help='x %(prog)s %(default)s %(type)s %%'),
         Sig('-y', action='store_const', default=42, const='XXX',
             help='y %(prog)s %(default)s %(const)s'),
@@ -3770,6 +3770,9 @@ class TestInvalidArgumentConstructors(TestCase):
         self.assertValueError('--')
         self.assertValueError('---')
 
+    def test_invalid_type(self):
+        self.assertValueError('--foo', type='int')
+
     def test_invalid_action(self):
         self.assertValueError('-x', action='foo')
         self.assertValueError('foo', action='baz')