Refactor the pretty printer to make it more flexible.

Instead of numerous booleans that steer the pretty printer, let the
caller pass on the desired transformation function.

Main.py

@@ -9,7 +9,7 @@ from DepCommand import DepCommand
 import Config
 from DoCommand import DoCommand
 from ListCommand import ListCommand
-from PrettyPrinter import pretty_print
+from PrettyPrinter import *
 from PriorityCommand import PriorityCommand
 import TodoFile
 import TodoList
@@ -59,7 +59,7 @@ class Application(object): # TODO: rename to CLIApplication
     def print_todo(self, p_number):
         """ Prints a single todo item to the standard output. """
         todo = self.todolist.todo(p_number)
-        printed = pretty_print([todo], True, True)
+        printed = pretty_print([todo], [pp_number, pp_color])
         print printed[0]
 
     def add(self):

PrettyPrinter.py

@@ -13,27 +13,48 @@ PRIORITY_COLORS = {
 PROJECT_COLOR = '\033[31m' # red
 NEUTRAL_COLOR = '\033[0m'
 
-def add_colors(p_todo_str, p_todo):
-    """ Adds colors to the todo string by inserting ANSI codes. """
+def pp_color(p_todo_str, p_todo):
+    """
+    Adds colors to the todo string by inserting ANSI codes.
+
+    Should be passed as a filter in the filter list of pretty_print()
+    """
 
-    color = NEUTRAL_COLOR
-    try:
-        color = PRIORITY_COLORS[p_todo.priority()]
-    except KeyError:
-        pass
+    if Config.COLORS:
+        color = NEUTRAL_COLOR
+        try:
+            color = PRIORITY_COLORS[p_todo.priority()]
+        except KeyError:
+            pass
 
-    p_todo_str = '%s%s%s' % (color, p_todo_str, NEUTRAL_COLOR)
+        p_todo_str = '%s%s%s' % (color, p_todo_str, NEUTRAL_COLOR)
 
-    if Config.HIGHLIGHT_PROJECTS_CONTEXTS:
-        p_todo_str = re.sub(r'\B(\+|@)\S+', PROJECT_COLOR + r'\g<0>' + color, \
-            p_todo_str)
+        if Config.HIGHLIGHT_PROJECTS_CONTEXTS:
+            p_todo_str = re.sub(r'\B(\+|@)\S+', PROJECT_COLOR + r'\g<0>' + color, \
+                p_todo_str)
 
     return p_todo_str
 
-def pretty_print(p_todos, p_show_numbers=False, p_color=False):
+def pp_number(p_todo_str, p_todo):
+    """
+    Inserts the todo number at the start of the string.
+
+    Should be passed as a filter in the filter list of pretty_print()
+    """
+    return "%3d %s" % (p_todo.attributes['number'], p_todo_str)
+
+def pretty_print(p_todos, p_filters=[]):
     """
     Given a list of todo items, pretty print it and return a list of
     formatted strings.
+
+    p_filters is a list of functions that transform the output string, each
+    function accepting two arguments:
+
+    * the todo's text that has to be modified;
+    * the todo object itself which allows for obtaining relevant information.
+
+    Examples are pp_color and pp_number in this file.
     """
 
     result = []
@@ -41,11 +62,8 @@ def pretty_print(p_todos, p_show_numbers=False, p_color=False):
     for todo in p_todos:
         todo_str = str(todo)
 
-        if p_show_numbers:
-            todo_str = "%3d %s" % (todo.attributes['number'], todo_str)
-
-        if Config.COLORS and p_color:
-            todo_str = add_colors(todo_str, todo)
+        for f in p_filters:
+            todo_str = f(todo_str, todo)
 
         result.append(todo_str)
 

View.py

 """ A view is a list of todos, sorted and filtered. """
 
-from PrettyPrinter import pretty_print
+from PrettyPrinter import *
 
 class View(object):
     """
@@ -28,7 +28,7 @@ class View(object):
 
     def pretty_print(self):
         """ Pretty prints the view. """
-        return '\n'.join(pretty_print(self._viewdata, True, True))
+        return '\n'.join(pretty_print(self._viewdata, [pp_number, pp_color]))
 
     def __str__(self):
         return '\n'.join(pretty_print(self._viewdata))