Create placeholder for args in aliases

With this change there is now possible to forward args supplied on CLI
to desired placed in real command.

Example config:

[aliases]
star = tag {} star 1
unstar = tag {} star

Example usage:

`topydo star foo` will resolve to: `topydo tag foo star 1`
`topydo unstar foo` will resolve to: `topydo tag foo star`

test/data/aliases.conf

@@ -3,3 +3,4 @@ foo = rm -f test
 baz = FooBar
 format = ls -F "|I| x c d {(}p{)} s k" -n 25
 smile = ls ☻
+star = tag {} star 1

test/test_get_sub_command.py

@@ -22,6 +22,7 @@ from topydo.commands.AddCommand import AddCommand
 from topydo.commands.DeleteCommand import DeleteCommand
 from topydo.commands.ListCommand import ListCommand
 from topydo.commands.ListProjectCommand import ListProjectCommand
+from topydo.commands.TagCommand import TagCommand
 from topydo.lib.Config import config
 
 class GetSubcommandTest(TopydoTest):
@@ -60,6 +61,14 @@ class GetSubcommandTest(TopydoTest):
         self.assertTrue(issubclass(real_cmd, ListCommand))
         self.assertEqual(final_args, [u"\u263b"])
 
+    def test_alias04(self):
+        config("test/data/aliases.conf")
+
+        args = ["star", "foo"]
+        real_cmd, final_args = get_subcommand(args)
+        self.assertTrue(issubclass(real_cmd, TagCommand))
+        self.assertEqual(final_args, ["foo", "star", "1"])
+
     def test_default_cmd01(self):
         args = ["bar"]
         real_cmd, final_args = get_subcommand(args)

topydo.conf

@@ -53,6 +53,8 @@ append_parent_contexts      = 0
 ;showall = ls -x
 ;next = ls -n 1
 ;top = ls -F '%I %x %P %S %k	%{(}H{)}' -N
+;star = tag {} star 1
+;unstar = tag {} star
 ;lsproj = lsprj
 ;listprj = lsprj
 ;listproj = lsprj

topydo/Commands.py

@@ -71,6 +71,18 @@ def get_subcommand(p_args):
         __import__(modulename, globals(), locals(), [classname], 0)
         return getattr(sys.modules[modulename], classname)
 
+    def join_args(p_cli_args, p_alias_args):
+        """
+        Returns properly joined args from alias definition and from user input.
+        """
+        if '{}' in p_alias_args:
+            pos = p_alias_args.index('{}')
+            args = p_alias_args[:pos] + p_cli_args + p_alias_args[pos+1:]
+        else:
+            args = p_alias_args + p_cli_args
+
+        return args
+
     def resolve_alias(p_alias, p_args):
         """
         Resolves a subcommand alias and returns a tuple (Command, args).
@@ -81,7 +93,7 @@ def get_subcommand(p_args):
         real_subcommand, alias_args = alias_map[p_alias]
         try:
             result = import_subcommand(real_subcommand)
-            args = alias_args + p_args
+            args = join_args(p_args, alias_args)
             return (result, args)
         except KeyError:
             return get_subcommand(['help'])