changeset:   78821:1b614921aefa
branch:      3.2
parent:      78818:c0c7b1998306
user:        R David Murray <rdmurray@bitdance.com>
date:        Fri Aug 31 22:45:20 2012 -0400
files:       Lib/argparse.py Lib/test/test_argparse.py Misc/ACKS Misc/NEWS
description:
#12776,#11839: call argparse type function only once.

Before, the type function was called twice in the case where the default
was specified and the argument was given as well.  This was especially
problematic for the FileType type, as a default file would always be
opened, even if a file argument was specified on the command line.

Patch by Arnaud Fontaine, with additional test by Mike Meyer.


diff -r c0c7b1998306 -r 1b614921aefa Lib/argparse.py
--- a/Lib/argparse.py	Fri Aug 31 17:11:39 2012 -0400
+++ b/Lib/argparse.py	Fri Aug 31 22:45:20 2012 -0400
@@ -1714,10 +1714,7 @@
             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, str):
-                            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:
@@ -1945,12 +1942,22 @@
         if positionals:
             self.error(_('too few arguments'))
 
-        # make sure all required actions were present
+        # make sure all required actions were present, and convert defaults.
         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:
+                    # 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 -r c0c7b1998306 -r 1b614921aefa Lib/test/test_argparse.py
--- a/Lib/test/test_argparse.py	Fri Aug 31 17:11:39 2012 -0400
+++ b/Lib/test/test_argparse.py	Fri Aug 31 22:45:20 2012 -0400
@@ -1462,6 +1462,22 @@
         ('readonly', NS(x=None, spam=RFile('readonly'))),
     ]
 
+class TestFileTypeDefaults(TempDirMixin, ParserTestCase):
+    """Test that a file is not created unless the default is needed"""
+    def setUp(self):
+        super(TestFileTypeDefaults, self).setUp()
+        file = open(os.path.join(self.temp_dir, 'good'), 'w')
+        file.write('good')
+        file.close()
+
+    argument_signatures = [
+        Sig('-c', type=argparse.FileType('r'), default='no-file.txt'),
+    ]
+    # should provoke no such file error
+    failures = ['']
+    # should not provoke error because default file is created
+    successes = [('-c good', NS(c=RFile('good')))]
+
 
 class TestFileTypeRB(TempDirMixin, ParserTestCase):
     """Test the FileType option/argument type for reading files"""
@@ -4468,6 +4484,38 @@
         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 -r c0c7b1998306 -r 1b614921aefa Misc/ACKS
--- a/Misc/ACKS	Fri Aug 31 17:11:39 2012 -0400
+++ b/Misc/ACKS	Fri Aug 31 22:45:20 2012 -0400
@@ -305,6 +305,7 @@
 Frederik Fix
 Matt Fleming
 Hernán Martínez Foffani
+Arnaud Fontaine
 Michael Foord
 Amaury Forgeot d'Arc
 Doug Fort
diff -r c0c7b1998306 -r 1b614921aefa Misc/NEWS
--- a/Misc/NEWS	Fri Aug 31 17:11:39 2012 -0400
+++ b/Misc/NEWS	Fri Aug 31 22:45:20 2012 -0400
@@ -112,6 +112,12 @@
 Library
 -------
 
+- Issue #12776,#11839: call argparse type function (specified by add_argument)
+  only once. Before, the type function was called twice in the case where the
+  default was specified and the argument was given as well.  This was
+  especially problematic for the FileType type, as a default file would always
+  be opened, even if a file argument was specified on the command line.
+
 - Issue #13370: Ensure that ctypes works on Mac OS X when Python is
   compiled using the clang compiler