# HG changeset patch
# User Arnaud Fontaine <arnau@debian.org>
# Date 1322193971 -32400
# Branch 2.7
# Node ID 3837457f1d3049492fe7ae5f2135e949cdbe85e4
# Parent  d1bdafa161e7aed2e6fa070d3cca7e244f458409
#12776: call argparse type function (specified by add_argument) only once.

diff --git a/Lib/argparse.py b/Lib/argparse.py
--- a/Lib/argparse.py
+++ b/Lib/argparse.py
@@ -1705,10 +1705,7 @@
             if action.dest is not SUPPRESS:
                 if not hasattr(namespace, action.dest):
                     if action.default is not SUPPRESS:
-                        default = action.default
-                        if isinstance(action.default, basestring):
-                            default = self._get_value(action, default)
-                        setattr(namespace, action.dest, default)
+                        setattr(namespace, action.dest, action.default)
 
         # add any parser defaults that aren't present
         for dest in self._defaults:
@@ -1936,12 +1933,24 @@
         if positionals:
             self.error(_('too few arguments'))
 
-        # make sure all required actions were present
+        # make sure all required actions were present and also convert
+        # action defaults which were not given as arguments
         for action in self._actions:
-            if action.required:
-                if action not in seen_actions:
+            if action not in seen_actions:
+                if action.required:
                     name = _get_action_name(action)
                     self.error(_('argument %s is required') % name)
+                else:
+                    # If default specified (None means it was not), convert
+                    # action default now instead of doing it before parsing
+                    # arguments to avoid calling convert functions twice
+                    # (which may fail) if the argument was given, but only
+                    # if it was defined already in the namespace
+                    if (action.default is not None and
+                        hasattr(namespace, action.dest) and
+                        action.default is getattr(namespace, action.dest)):
+                        setattr(namespace, action.dest,
+                                self._get_value(action, action.default))
 
         # make sure all required groups had one option present
         for group in self._mutually_exclusive_groups:
diff --git a/Lib/test/test_argparse.py b/Lib/test/test_argparse.py
--- a/Lib/test/test_argparse.py
+++ b/Lib/test/test_argparse.py
@@ -4416,6 +4416,38 @@
         else:
             self.fail()
 
+# ================================================
+# Check that the type function is called only once
+# ================================================
+
+class TestTypeFunctionCallOnlyOnce(TestCase):
+
+    def test_type_function_call_only_once(self):
+        def spam(string_to_convert):
+            self.assertEqual(string_to_convert, 'spam!')
+            return 'foo_converted'
+
+        parser = argparse.ArgumentParser()
+        parser.add_argument('--foo', type=spam, default='bar')
+        args = parser.parse_args('--foo spam!'.split())
+        self.assertEqual(NS(foo='foo_converted'), args)
+
+# ================================================================
+# Check that the type function is called with a non-string default
+# ================================================================
+
+class TestTypeFunctionCallWithNonStringDefault(TestCase):
+
+    def test_type_function_call_with_non_string_default(self):
+        def spam(int_to_convert):
+            self.assertEqual(int_to_convert, 0)
+            return 'foo_converted'
+
+        parser = argparse.ArgumentParser()
+        parser.add_argument('--foo', type=spam, default=0)
+        args = parser.parse_args([])
+        self.assertEqual(NS(foo='foo_converted'), args)
+
 # ======================
 # parse_known_args tests
 # ======================
diff --git a/Misc/ACKS b/Misc/ACKS
--- a/Misc/ACKS
+++ b/Misc/ACKS
@@ -935,3 +935,4 @@
 Uwe Zessin
 Tarek Ziadé
 Peter Åstrand
+Arnaud Fontaine
diff --git a/Misc/NEWS b/Misc/NEWS
--- a/Misc/NEWS
+++ b/Misc/NEWS
@@ -79,6 +79,10 @@
 Library
 -------
 
+- Issue #12776: call argparse type function (specified by add_argument)
+  only once. Before, type function was called twice in case the default
+  was specified and the argument was given as well.
+
 - Issue #13458: Fix a memory leak in the ssl module when decoding a
   certificate with a subjectAltName.  Patch by Robert Xiao.