Python: Command Pattern

GeovinDuCommand.py

# 命令模式 Command  Pattern  GeovinDuCommand.py

# Web Browser:
class WebBrowser(object):
    def __init__(self):
        self.bookmarks = []
        self.currentUrl = None

    def Navigate(self, url):
        self.currentUrl = url

    def BookmarkCurrentPage(self):
        valid = self.currentUrl is not None
        contains = self.currentUrl in self.bookmarks
        if valid and not contains:
            self.bookmarks.append(self.currentUrl)

    def RemoveBookmark(self, url):
        self.bookmarks.remove(url)

    def PrintBookmarks(self):
        print("书签:")
        for i in self.bookmarks:
            print("\t" + str(i))

# AddBookmarkCommand:
class AddBookmarkCommand(object):
   def __init__(self, webBrowser):
       self.webBrowser = webBrowser
       self.url = None

   def Execute(self):
       self.url = self.webBrowser.currentUrl
       self.webBrowser.BookmarkCurrentPage()

   def Undo(self):
       self.webBrowser.RemoveBookmark(self.url)

   def Redo(self):
       self.Execute()

# Bookmarker:
class Bookmarker(object):
   def __init__(self, webBrowser):
       self.webBrowser = webBrowser
       self.undoStack = []
       self.redoStack = []

   def BookmarkCurrentPage(self):
       command = AddBookmarkCommand(self.webBrowser)
       self.undoStack.append(command)
       self.redoStack = []

       command.Execute()

   def UndoBookmark(self):
       if len(self.undoStack) != 0:
           command = self.undoStack.pop()
           self.redoStack.append(command)

           command.Undo()

   def RedoBookmark(self):
       if len(self.redoStack) != 0:
           command = self.redoStack.pop()
           self.undoStack.append(command)

           command.Redo()

# 2 geovindu
class data:
    _data = 0

    def __init__(self, value=0) -> None:
        data._data += value


    def add(self):
        pass


    def subtract(self):
        pass

    def __str__(self) -> str:
        return f"现值: {data._data}"


class Addition(data):
    def __init__(self, value=0) -> None:
        super().__init__(value)

    def add(self, value):
        data._data += value
        print("正在执行加法操作...")

    def __str__(self) -> str:
        return super().__str__()


class Subtraction(data):
    def __init__(self, value=0) -> None:
        super().__init__(value)

    def subtract(self, value):
        data._data -= value
        print("正在进行减法运算...")

    def __str__(self) -> str:
        return super().__str__()

class Command():

    def execute(self):
        pass


    def undo(self):
        pass

class AdditionCommand(Command):
    def __init__(self, obj, value):
        self.obj = obj
        self.value = value

    def execute(self):
        self.obj.add(self.value)

    def undo(self, commandObj):
        commandObj.set_command(SubtractionCommand(Subtraction(), self.value))
        commandObj.invoke()


class SubtractionCommand(Command):
    def __init__(self, obj, value):
        self.obj = obj
        self.value = value

    def execute(self):
        self.obj.subtract(self.value)

    def undo(self, commandObj):
        commandObj.set_command(AdditionCommand(Addition(), self.value))
        commandObj.invoke()


class ActionInvoker:
    def __init__(self, command):
        self.command = command

    def set_command(self, command):
        self.command = command

    def invoke(self):
        self.command.execute()

    def undo(self):
        print("[!UNDO] ", end="")
        self.command.undo(self)

main.py 调用

# 命令模式 Command  Pattern

memeSurfer = GeovinDuCommand.WebBrowser()

bookmarker = GeovinDuCommand.Bookmarker(memeSurfer)

memeSurfer.Navigate("geovindu.gov")
bookmarker.BookmarkCurrentPage()

memeSurfer.PrintBookmarks()

memeSurfer.Navigate("dusystem.com")
bookmarker.BookmarkCurrentPage()

memeSurfer.PrintBookmarks()

bookmarker.UndoBookmark()

memeSurfer.PrintBookmarks()

bookmarker.RedoBookmark()

memeSurfer.PrintBookmarks()
print("\n")
obj = GeovinDuCommand.data(100)
print(obj)
command_addition = GeovinDuCommand.AdditionCommand(GeovinDuCommand.Addition(), 10) # concrete command
command_subtraction = GeovinDuCommand.SubtractionCommand(GeovinDuCommand.Subtraction(), 10) # concrete command

action_invoker = GeovinDuCommand.ActionInvoker(command_addition); # invoker
action_invoker.invoke()
print(obj)

action_invoker.set_command(command_subtraction)
action_invoker.invoke()
print(obj)

action_invoker.undo()
print(obj)
action_invoker.undo()
print(obj)

输出：

书签:
	geovindu.gov
书签:
	geovindu.gov
	dusystem.com
书签:
	geovindu.gov
书签:
	geovindu.gov
	dusystem.com


现值: 100
正在执行加法操作...
现值: 110
正在进行减法运算...
现值: 100
[!UNDO] 正在执行加法操作...
现值: 110
[!UNDO] 正在进行减法运算...
现值: 100

Process finished with exit code 0