implemented command pattern.

pypatterns/behavioral/command.py

@@ -0,0 +1,94 @@
+from abc import ABCMeta, abstractmethod
+
+
+class InvalidActionException(Exception):
+    """
+    Exception for when an invalid action is called on a Receiver.
+    """
+    pass
+
+
+class InvalidInvokerCommandException(Exception):
+    """
+    Exception for when an invalid command is given to an Invoker to execute.
+    """
+
+
+class Receiver(object, metaclass=ABCMeta):
+    """
+    Abstract receiver class as part of the Command pattern.
+    """
+    def action(self, name, *args, **kwargs):
+        """
+        Delegates which method to be called for a desired action.
+
+        @param name: The name of the action to execute.
+        @type name: str
+        @param args: Any arguments for the action.
+        @param kwargs: Any keyword arguments for the action.
+        """
+        try:
+            return getattr(self, name)(*args, **kwargs)
+        except AttributeError:
+            raise InvalidActionException
+
+
+class Command(object, metaclass=ABCMeta):
+    """
+    Abstract Command class as part of the Command pattern.
+    """
+    def __init__(self, receiver):
+        """
+        Initialize a new command instance.
+
+        @param receiver: The receiver for this command to use.
+        @type receiver: Receiver
+        """
+        self._receiver = receiver
+
+    @abstractmethod
+    def execute(self):
+        """
+        Abstract method for executing an action.
+        """
+        pass
+
+    @abstractmethod
+    def unexecute(self):
+        """
+        Abstract method for unexecuting an action.
+        """
+        pass
+
+
+class Invoker(object, metaclass=ABCMeta):
+    """
+    Abstract Invoker class as part of the Command pattern.
+    """
+    def __init__(self, valid_commands):
+        """
+        Initialize a new Invoker instance.
+
+        @param valid_commands: A list of command classes this invoker can handle.
+        """
+        self._history = []
+        self._valid_commands = valid_commands
+
+    def execute(self, command):
+        """
+        Execute a command.
+
+        @param command: A command for the invoker to execute.
+        @type command: Command
+        """
+        if command.__class__ not in self._valid_commands:
+            raise InvalidInvokerCommandException
+        else:
+            self._history.append(command)
+            return command.execute()
+
+    def undo(self):
+        """
+        Undo the last command.
+        """
+        return self._history.pop().unexecute()