Introduce new MultiCommand class.

It will be common for all commands operating with multiple todo IDs.

topydo/lib/MultiCommand.py

+# Topydo - A todo.txt client written in Python.
+# Copyright (C) 2014 - 2015 Bram Schoenmakers <me@bramschoenmakers.nl>
+#
+# This program is free software: you can redistribute it and/or modify
+# it under the terms of the GNU General Public License as published by
+# the Free Software Foundation, either version 3 of the License, or
+# (at your option) any later version.
+#
+# This program is distributed in the hope that it will be useful,
+# but WITHOUT ANY WARRANTY; without even the implied warranty of
+# MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
+# GNU General Public License for more details.
+#
+# You should have received a copy of the GNU General Public License
+# along with this program.  If not, see <http://www.gnu.org/licenses/>.
+
+from topydo.lib.Command import Command
+from topydo.lib.TodoListBase import InvalidTodoException
+
+class MultiCommand(Command):
+    """
+    A common class for operations that can work with multiple todo IDs.
+    """
+
+    def __init__(self, p_args, p_todolist,
+                 p_out=lambda a: None,
+                 p_err=lambda a: None,
+                 p_prompt=lambda a: None):
+        super(MultiCommand, self).__init__(
+            p_args, p_todolist, p_out, p_err, p_prompt)
+
+        self.todos = []
+        self.invalid_numbers = []
+
+    def get_todos(self, p_numbers):
+        """ Gets todo objects from supplied todo IDs """
+        for number in p_numbers:
+            try:
+                self.todos.append(self.todolist.todo(number))
+            except InvalidTodoException:
+                self.invalid_numbers.append(number)
+
+    def catch_todo_errors(self):
+        """
+        Returns None or list of error messages depending on number of valid todo
+        objects and number of invalid todo IDs.
+
+        In case of multiple invalid todo IDs we generate separate error message for each
+        one of them with information about supplied ID.
+        """
+        errors = []
+
+        if len(self.invalid_numbers) > 1 or len(self.invalid_numbers) > 0 and len(self.todos) > 0:
+            for number in self.invalid_numbers:
+                errors.append("Invalid todo number given: {}.".format(number))
+        elif len(self.invalid_numbers) == 1 and len(self.todos) == 0:
+            errors.append("Invalid todo number given.")
+        elif len(self.todos) == 0 and len(self.invalid_numbers) == 0:
+            errors.append(self.usage())
+
+        if len(errors) > 0:
+            return errors
+        else:
+            return None