Add view method.

TodoList.py

+"""
+A list of todo items.
+"""
+
+class TodoList(object):
+    """
+    Provides operations for a todo list, such as adding items, removing them,
+    etc.
+
+    The list is usually a complete list found in the program's input (e.g. a
+    todo.txt file), not an arbitrary set of todo items.
+    """
+    _todos = []
+
+    def __init__(self, todos):
+        """
+        Should be given a list of Todo objects (already read and parsed from
+        file or standard input.
+        """
+        self._todos = todos
+
+    def todo(self, p_number):
+        """
+        The _todos list has the same order as in the backend store (usually
+        a todo.txt file. The user refers to the first task as number 1, so use
+        index 0, etc.
+        """
+        result = None
+        try:
+            result = self._todos[p_number - 1]
+        except IndexError:
+            result = None
+
+        return result
+
+    def todos(self):
+        """ Returns the list of all todos. """
+        return self._todos
+
+    def add(self, p_item):
+        """
+        Given a Todo(Base) item, add it to the end of the list.
+        """
+        self._todos.append(p_item)
+
+    def delete(self, p_number):
+        """ Deletes a todo item from the list. """
+        del self._todos[p_number - 1]
+
+    def append(self, p_number, p_string):
+        """
+        Appends a text to the todo, specified by its number.
+        The todo will be parsed again, such that tags and projects in de
+        appended string are processed.
+        """
+        if len(p_string) > 0:
+            todo = self.todo(p_number)
+            new_text = todo.text() + ' ' + p_string
+            todo.set_text(new_text)
+
+    def set_completed(self, p_number):
+        """ Marks the todo with the given number as complete. """
+        self.todo(p_number).set_completed()
+
+    def projects(self):
+        """ Returns a set of all projects in this list. """
+        result = set()
+        for todo in self._todos:
+            projects = todo.projects()
+            result = result.union(projects)
+
+    def contexts(self):
+        """ Returns a set of all contexts in this list. """
+        result = set()
+        for todo in self._todos:
+            contexts = todo.contexts()
+            result = result.union(contexts)
+
+    def set_priority(self, p_number, p_priority):
+        """ Sets the priority of the todo with the given number. """
+        self.todo(p_number).set_priority(p_priority)
+
+    def view(self, p_sorter, p_filter):
+        """
+        Constructs a view of the todo list.
+
+        A view is a sorted and filtered todo list, where the properties are
+        defined by the end user. Todos is this list should not be modified,
+        modifications should occur through this class.
+        """
+        return p_filter.filter(p_sorter.sort(self._todos))
+
+    def __print__(self):
+        result = ""
+        for todo in self._todos:
+            result = "%s" % todo
+
+        return result
+