Speed up topydo a bit by only loading the necessary subcommand module.

topydo was a tad slow, because all modules of all subcommands were
loaded with each invocation of topydo. Particularly, the ical subcommand
was quite slow because it loads modules from the icalendar package.

topydo/Commands.py

@@ -19,51 +19,36 @@ This module is aware of all supported submodules and hands out a Command
 instance based on an argument list.
 """
 
-from topydo.lib.Config import config
+import sys
 
-from topydo.commands.AddCommand import AddCommand
-from topydo.commands.AppendCommand import AppendCommand
-from topydo.commands.DeleteCommand import DeleteCommand
-from topydo.commands.DepCommand import DepCommand
-from topydo.commands.DepriCommand import DepriCommand
-from topydo.commands.DoCommand import DoCommand
-from topydo.commands.EditCommand import EditCommand
-from topydo.commands.ExitCommand import ExitCommand
-from topydo.commands.IcalCommand import IcalCommand
-from topydo.commands.ListCommand import ListCommand
-from topydo.commands.ListContextCommand import ListContextCommand
-from topydo.commands.ListProjectCommand import ListProjectCommand
-from topydo.commands.PostponeCommand import PostponeCommand
-from topydo.commands.PriorityCommand import PriorityCommand
-from topydo.commands.SortCommand import SortCommand
-from topydo.commands.TagCommand import TagCommand
+from topydo.lib.Config import config
 
 _SUBCOMMAND_MAP = {
-    'add': AddCommand,
-    'app': AppendCommand,
-    'append': AppendCommand,
-    'del': DeleteCommand,
-    'dep': DepCommand,
-    'depri': DepriCommand,
-    'do': DoCommand,
-    'edit': EditCommand,
-    'exit': ExitCommand, # used for the prompt
-    'ical': IcalCommand,
-    'ls': ListCommand,
-    'lscon': ListContextCommand,
-    'listcon': ListContextCommand,
-    'lsprj': ListProjectCommand,
-    'lsproj': ListProjectCommand,
-    'listprj': ListProjectCommand,
-    'listproj': ListProjectCommand,
-    'listproject': ListProjectCommand,
-    'listprojects': ListProjectCommand,
-    'postpone': PostponeCommand,
-    'pri': PriorityCommand,
-    'quit': ExitCommand,
-    'rm': DeleteCommand,
-    'sort': SortCommand,
-    'tag': TagCommand,
+    'add': 'AddCommand',
+    'app': 'AppendCommand',
+    'append': 'AppendCommand',
+    'del': 'DeleteCommand',
+    'dep': 'DepCommand',
+    'depri': 'DepriCommand',
+    'do': 'DoCommand',
+    'edit': 'EditCommand',
+    'exit': 'ExitCommand', # used for the prompt
+    'ical': 'IcalCommand',
+    'ls': 'ListCommand',
+    'lscon': 'ListContextCommand',
+    'listcon': 'ListContextCommand',
+    'lsprj': 'ListProjectCommand',
+    'lsproj': 'ListProjectCommand',
+    'listprj': 'ListProjectCommand',
+    'listproj': 'ListProjectCommand',
+    'listproject': 'ListProjectCommand',
+    'listprojects': 'ListProjectCommand',
+    'postpone': 'PostponeCommand',
+    'pri': 'PriorityCommand',
+    'quit': 'ExitCommand',
+    'rm': 'DeleteCommand',
+    'sort': 'SortCommand',
+    'tag': 'TagCommand',
 }
 
 def get_subcommand(p_args):
@@ -81,6 +66,18 @@ def get_subcommand(p_args):
     If no valid command could be found, the subcommand part of the tuple
     is None.
     """
+    def import_subcommand(p_subcommand):
+        """
+        Returns the class of the requested subcommand. An invalid p_subcommand
+        will result in an ImportError, since this is a programming mistake
+        (most likely an error in the _SUBCOMMAND_MAP).
+        """
+        classname = _SUBCOMMAND_MAP[p_subcommand]
+        modulename = 'topydo.commands.{}'.format(classname)
+
+        __import__(modulename, globals(), locals(), [classname], -1)
+        return getattr(sys.modules[modulename], classname)
+
     result = None
     args = p_args
 
@@ -88,7 +85,7 @@ def get_subcommand(p_args):
         subcommand = p_args[0]
 
         if subcommand in _SUBCOMMAND_MAP:
-            result = _SUBCOMMAND_MAP[subcommand]
+            result = import_subcommand(subcommand)
             args = args[1:]
         elif subcommand == 'help':
             try:
@@ -103,12 +100,12 @@ def get_subcommand(p_args):
         else:
             p_command = config().default_command()
             if p_command in _SUBCOMMAND_MAP:
-                result = _SUBCOMMAND_MAP[p_command]
+                result = import_subcommand(p_command)
                 # leave args unchanged
     except IndexError:
         p_command = config().default_command()
         if p_command in _SUBCOMMAND_MAP:
-            result = _SUBCOMMAND_MAP[p_command]
+            result = import_subcommand(p_command)
 
     return (result, args)