Default subcommand if no one specified

komandr.py

@@ -7,7 +7,7 @@
 import inspect
 import argparse
 from functools import wraps
-from itertools import izip_longest
+from itertools import izip_longest, chain
 
 
 class prog(object):
@@ -102,15 +102,27 @@ def execute(self, arg_list):
         :param type: list
 
         """
+        if getattr(self, 'default_subcommand', None):
+            subcommand = arg_list[0] if arg_list else ''
+            action_option_strings = chain.from_iterable(i.option_strings
+                    for i in self.parser._actions)
+            if not (subcommand
+                    and subcommand in self.subparsers.choices
+                    or subcommand in action_option_strings):
+                arg_list[:0] = [self.default_subcommand]
+
         arg_map = self.parser.parse_args(arg_list).__dict__
         command = arg_map.pop(self._COMMAND_FLAG)
         return command(**arg_map)
 
-    def __call__(self):
+    def __call__(self, default_subcommand=None):
         """Calls :py:func:``execute`` with :py:class:``sys.argv`` excluding
         script name which comes first.
 
+        :param default: name of subcommand called if no subcommand specified.
+        :param type: str
         """
+        self.default_subcommand = default_subcommand
         self.execute(sys.argv[1:])
 
 main = prog()

tests.py

@@ -1,10 +1,14 @@
 # TODO: Add much more tests
 import unittest
 import komandr
+from mock import patch
 
 
 class TestKomandr(unittest.TestCase):
 
+    def tearDown(self):
+        komandr.main.default_subcommand = None
+
     def testCommand(self):
         def foo(bar, baz=None):
             return bar, baz
@@ -13,5 +17,44 @@ def foo(bar, baz=None):
                          komandr.execute(['foo', '1', '--baz', '2']))
 
 
+    def testDefaultSubcommand(self):
+        def foo(bar, baz=None):
+            return bar, baz
+        komandr.command(foo)
+
+        # Without main.default_subcommand a `SystemExit` exception would raise.
+        with self.assertRaises(SystemExit) as ex:
+            komandr.execute([])
+
+        self.assertEqual(2, ex.exception.code)
+
+        # With main.default_subcommand='foo', subcommand named `foo` would be
+        # called by default when no subcommand.
+        komandr.main.default_subcommand = 'foo'
+        self.assertEqual(('1', '2'), komandr.execute(['1', '--baz', '2']))
+
+    def testDefaultSubcommandWithoutOptions(self):
+        def foo():
+            return 'bar'
+        komandr.command(foo)
+
+        komandr.main.default_subcommand = 'foo'
+        self.assertEqual('bar', komandr.execute([]))
+
+    def testOptionsNotTriggerDefaultSubcommand(self):
+        def foo(baz='bar'):
+            return baz
+        komandr.command(foo)
+
+        komandr.main.default_subcommand = 'foo'
+        with patch.object(komandr.main.parser, 'print_help') as mock:
+            with self.assertRaises(SystemExit) as ex:
+                komandr.execute(['--help'])
+
+        self.assertEqual(0, ex.exception.code)
+        self.assertTrue(mock.called)
+
+        self.assertEqual('bar baz', komandr.execute(['--baz', 'bar baz']))
+
 if __name__ == '__main__':
     unittest.main()