From: Barry Warsaw <barry@python.org>
Date: Wed, 12 Sep 2012 02:38:47 +0000 (-0400)
Subject: - Issue #15906: Fix a regression in argparse caused by the preceding change,
X-Git-Tag: v3.3.1rc1~813^2~82
X-Git-Url: https://granicus.if.org/sourcecode?a=commitdiff_plain;h=4b2f9e914d497d6b2b5ec09a03da8b6f171dffed;p=python

- Issue #15906: Fix a regression in argparse caused by the preceding change,
  when action='append', type='str' and default=[].
---

diff --git a/Lib/argparse.py b/Lib/argparse.py
index 52ed3ab107..fba6a262f5 100644
--- a/Lib/argparse.py
+++ b/Lib/argparse.py
@@ -1957,6 +1957,7 @@ class ArgumentParser(_AttributeHolder, _ActionsContainer):
                     # 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
+                            isinstance(action, _StoreAction) and
                             hasattr(namespace, action.dest) and
                             action.default is getattr(namespace, action.dest)):
                         setattr(namespace, action.dest,
diff --git a/Lib/test/test_argparse.py b/Lib/test/test_argparse.py
index a2f9a69a59..cd80dc6d16 100644
--- a/Lib/test/test_argparse.py
+++ b/Lib/test/test_argparse.py
@@ -4516,6 +4516,16 @@ class TestTypeFunctionCallWithNonStringDefault(TestCase):
         args = parser.parse_args([])
         self.assertEqual(NS(foo='foo_converted'), args)
 
+    def test_issue_15906(self):
+        # Issue #15906: When action='append', type=str, default=[] are
+        # providing, the dest value was the string representation "[]" when it
+        # should have been an empty list.
+        parser = argparse.ArgumentParser()
+        parser.add_argument('--test', dest='test', type=str,
+                            default=[], action='append')
+        args = parser.parse_args([])
+        self.assertEqual(args.test, [])
+
 # ======================
 # parse_known_args tests
 # ======================
diff --git a/Misc/NEWS b/Misc/NEWS
index 3b09e9633a..24c6b7121d 100644
--- a/Misc/NEWS
+++ b/Misc/NEWS
@@ -139,6 +139,9 @@ Library
   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 #15906: Fix a regression in argparse caused by the preceding change,
+  when action='append', type='str' and default=[].
+
 - Issue #13370: Ensure that ctypes works on Mac OS X when Python is
   compiled using the clang compiler