Speed up 'ls' a bit (and also lsprj, lscon).

This is achieved by importing some modules only when applicable. For
instance, 'ls' doesn't need ChangeSet and also doesn't always need
icalendar. Sorting and archiving is also only applicable to writing
commands (del, add, etc.).

topydo/cli/CLIApplicationBase.py

@@ -101,12 +101,9 @@ except ConfigError as config_error:
     error(str(config_error))
     sys.exit(1)
 
-from topydo.commands.ArchiveCommand import ArchiveCommand
-from topydo.commands.SortCommand import SortCommand
 from topydo.lib import TodoFile
 from topydo.lib import TodoList
 from topydo.lib import TodoListBase
-from topydo.lib.ChangeSet import ChangeSet
 from topydo.lib.Utils import escape_ansi
 
 
@@ -178,6 +175,7 @@ class CLIApplicationBase(object):
             self.backup.add_archive(archive)
 
         if archive:
+            from topydo.commands.ArchiveCommand import ArchiveCommand
             command = ArchiveCommand(self.todolist, archive)
             command.execute()
 
@@ -209,6 +207,8 @@ class CLIApplicationBase(object):
         """
         if config().backup_count() > 0 and p_command and not self.is_read_only(p_command):
             call = [p_command.__module__.lower()[16:-7]] + p_args # strip "topydo.commands" and "Command"
+
+            from topydo.lib.ChangeSet import ChangeSet
             self.backup = ChangeSet(self.todolist, p_call=call)
 
         command = p_command(
@@ -237,6 +237,7 @@ class CLIApplicationBase(object):
                 self._archive()
 
             if config().keep_sorted():
+                from topydo.commands.SortCommand import SortCommand
                 self._execute(SortCommand, [])
 
             if self.backup:

topydo/commands/ListCommand.py

@@ -16,8 +16,6 @@
 
 from topydo.lib.Config import config
 from topydo.lib.ExpressionCommand import ExpressionCommand
-from topydo.lib.IcalPrinter import IcalPrinter
-from topydo.lib.JsonPrinter import JsonPrinter
 from topydo.lib.PrettyPrinter import pretty_printer_factory
 from topydo.lib.PrettyPrinterFilter import (PrettyPrinterHideTagFilter,
                                             PrettyPrinterIndentFilter)
@@ -58,9 +56,11 @@ class ListCommand(ExpressionCommand):
                 self.sort_expression = value
             elif opt == '-f':
                 if value == 'json':
+                    from topydo.lib.JsonPrinter import JsonPrinter
                     self.printer = JsonPrinter()
                 elif value == 'ical':
                     if self._poke_icalendar():
+                        from topydo.lib.IcalPrinter import IcalPrinter
                         self.printer = IcalPrinter(self.todolist)
                 else:
                     self.printer = None