Let abstract implementations raise NotImplementedError.

topydo/commands/DCommand.py

@@ -44,8 +44,7 @@ class DCommand(MultiCommand):
         return ("", [])
 
     def process_flag(self, p_option, p_value):
-        """ Default implementation of processing specific flags. """
-        pass
+        raise NotImplementedError
 
     def process_flags(self):
         opts, args = self.get_flags()
@@ -71,11 +70,10 @@ class DCommand(MultiCommand):
         self.out(printer.print_list(p_todos))
 
     def prompt_text(self):
-        return "Yes or no? [y/N] "
+        raise NotImplementedError
 
     def prefix(self):
-        """ Prefix to use when printing a todo. """
-        return ""
+        raise NotImplementedError
 
     def _process_subtasks(self, p_todo):
         children = self._uncompleted_children(p_todo)
@@ -116,17 +114,17 @@ class DCommand(MultiCommand):
         return True
 
     def condition_failed_text(self):
-        return ""
+        raise NotImplementedError
 
     def execute_specific(self, _):
-        pass
+        raise NotImplementedError
 
     def execute_specific_core(self, p_todo):
         """
         The core operation on the todo itself. Also used to operate on
         child/parent tasks.
         """
-        pass
+        raise NotImplementedError
 
     def execute_multi_specific(self):
         old_active = self._active_todos()

topydo/commands/ListCommand.py

@@ -46,7 +46,7 @@ class ListCommand(ExpressionCommand):
         """
         try:
             import icalendar as _
-        except ImportError:
+        except ImportError: # pragma: no cover
             self.error("icalendar package is not installed.")
             return False
 
@@ -101,7 +101,7 @@ class ListCommand(ExpressionCommand):
 
         try:
             self._process_flags()
-        except SyntaxError:
+        except SyntaxError: # pragma: no cover
             # importing icalendar failed, most likely due to Python 3.2
             self.error("icalendar is not supported in this Python version.")
             return False

topydo/lib/Command.py

@@ -84,8 +84,10 @@ class Command(object):
         return result
 
     def usage(self):
-        return "No usage text available for this command."
+        """ Returns a one-line synopsis for this command. """
+        raise NotImplementedError
 
     def help(self):
-        return "No help text available for this command."
+        """ Returns the help text for this command. """
+        raise NotImplementedError
 

topydo/lib/Filter.py

@@ -29,8 +29,7 @@ class Filter(object):
         return [t for t in p_todos if self.match(t)]
 
     def match(self, _):
-        """ Default match value. """
-        return True
+        raise NotImplementedError
 
 class NegationFilter(Filter):
     def __init__(self, p_filter):

topydo/lib/PrettyPrinter.py

@@ -26,8 +26,7 @@ class Printer(object):
     Subclasses must at least implement the print_todo method.
     """
     def print_todo(self, p_todo):
-        """ Base implementation."""
-        return p_todo.source()
+        raise NotImplementedError
 
     def print_list(self, p_todos):
         """

topydo/lib/PrettyPrinterFilter.py

@@ -30,8 +30,10 @@ class PrettyPrinterFilter(object):
     """
 
     def filter(self, p_todo_str, _):
-        """ Default implementation returns an unmodified todo string. """
-        return p_todo_str
+        """
+        Applies a filter to p_todo_str and returns a modified version of it.
+        """
+        raise NotImplementedError
 
 class PrettyPrinterColorFilter(PrettyPrinterFilter):
     """