Fix a bug that was preventing % from being used in help messages.

2 files changed, 39 insertions, 5 deletions

diff --git a/argparse.py b/argparse.py
index 75a9043..ce1adb9 100644
--- a/argparse.py
+++ b/argparse.py
@@ -306,7 +306,7 @@ class HelpFormatter(object):
     # Help-formatting methods
     # =======================
     def format_help(self):
-        help = self._root_section.format_help() % dict(prog=self._prog)
+        help = self._root_section.format_help()
         if help:
             help = self._long_break_matcher.sub('\n\n', help)
             help = help.strip('\n') + '\n'
@@ -321,9 +321,13 @@ class HelpFormatter(object):
         if prefix is None:
             prefix = _('usage: ')
 
+        # if usage is specified, use that
+        if usage is not None:
+            usage = usage % dict(prog=self._prog)
+
         # if no optionals or positionals are available, usage is just prog
-        if usage is None and not actions:
-            usage = '%(prog)s'
+        elif usage is None and not actions:
+            usage = '%(prog)s' % dict(prog=self._prog)
 
         # if optionals and positionals are available, calculate usage
         elif usage is None:
diff --git a/test/test_argparse.py b/test/test_argparse.py
index 7536d5e..ba19835 100644
--- a/test/test_argparse.py
+++ b/test/test_argparse.py
@@ -3126,7 +3126,7 @@ class TestHelpVariableExpansion(HelpTestCase):
     parser_signature = Sig(prog='PROG')
     argument_signatures = [
         Sig('-x', type='int',
-            help='x %(prog)s %(default)s %(type)s'),
+            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'),
         Sig('--foo', choices='abc',
@@ -3154,7 +3154,7 @@ class TestHelpVariableExpansion(HelpTestCase):
 
         optional arguments:
           -h, --help     show this help message and exit
-          -x X           x PROG None int
+          -x X           x PROG None int %
           -y             y PROG 42 XXX
           --foo {a,b,c}  foo PROG None a, b, c
           --bar BBB      bar PROG baz bar
@@ -3166,6 +3166,36 @@ class TestHelpVariableExpansion(HelpTestCase):
     version = ''
 
 
+class TestHelpVariableExpansionUsageSupplied(HelpTestCase):
+    """Test that variables are expanded properly when usage= is present"""
+
+    parser_signature = Sig(prog='PROG', usage='%(prog)s FOO')
+    argument_signatures = []
+    argument_group_signatures = []
+    usage = ('''\
+        usage: PROG FOO
+        ''')
+    help = usage + '''\
+
+        optional arguments:
+          -h, --help  show this help message and exit
+        '''
+    version = ''
+
+
+class TestHelpVariableExpansionNoArguments(HelpTestCase):
+    """Test that variables are expanded properly with no arguments"""
+
+    parser_signature = Sig(prog='PROG', add_help=False)
+    argument_signatures = []
+    argument_group_signatures = []
+    usage = ('''\
+        usage: PROG
+        ''')
+    help = usage
+    version = ''
+
+
 class TestHelpSuppressUsage(HelpTestCase):
     """Test that items can be suppressed in usage messages"""