Function emulation using __call__，emulation__call_,A simple but

Function emulation using __call__，emulation__call_,A simple but

A simple but useful class that emulates a function to gracefully permit latentassignment. In other words, I can use the emulating class as a valid functionin assignments with the ability to later associate a function to perfrom theactual operations.

# This is the emulating class.class Function:    def __init__(self):        # Dummy function        self.function = lambda *args:None        self.menu = None        self.button = None        self.enabled = True    # This method causes the Function instances to be    # callable as though they were a function    def __call__(self, *args):        if self.enabled:            return self.function(*args)    def SetFunction(self, func):        self.function = func    def SetMenu(self, menu):        self.menu = menu        self.menu.Enable(self.enabled)    def SetButton(self, btn):        self.button = btn        self.button.Enable(self.enabled)    def Enable(self, on=True):        if self.menu:            self.menu.Enable(on)        if self.button:            self.button.Enable(on)        self.enabled = onclass FUNCTION_TABLE:    NewFile     = Function()    OpenFile    = Function()    SaveFile    = Function()    Exit        = Function()...    # Initializing the main wx.Frame...    item = wx.MenuItem( menu, id, "&Open", "Open a file" )    # Note that OpenFile will act as an event handler, but at this    # moment, no function has actually been assigned to handle the event    self.Bind( wx.EVT_MENU, FUNCTION_TABLE.OpenFile, id=id )    FUNCTION_TABLE.OpenFile.SetMenu( item )...    # Populating a wx.Panel (or similiar object) with controls, etc...    button = wx.Button( self, id, "Open File" )    button.Bind( wx.EVT_BUTTON, FUNCTION_TABLE.OpenFile )    FUNCTION_TABLE.OpenFile.SetButton( button )    # A function is finally assigned, but nobody is any the wiser.    # My button and my menu are still going to call the same thing.    # They don't know anything about self.OnOpenFile, nor do they     # need to.  They also don't know about each other!    FUNCTION_TABLE.OpenFile.SetFunction( self.OnOpenFile )...    # An event handler method of the wx.Panel...    def OnOpenFile(event):        ...

Background:

Using wxPython, I have multiple GUI controls accessing the same event handler.In this example, a menu item and a button both perform the same file openingoperation. Unfortunately, the menu is defined well before the panel with thebutton (and hence the event handler) is defined.

Solution:

Using this function table, I am able to give the menu item something to Bindto that I can later assign a function to when my panel is defined. This way mymenu definition doesn't need to know anything about my button, and vice versa.Each definition independently registers itself.

Another great benefit is the ability to tie these elements together in otherways. Continuing with the menu and button example, I can enable/disable bothof them through the same class. By making FUNCTION_TABLE visible throughout myprogram, I can easily enable/disable all controls associated with openingfiles without having to be able to see any particular control. How wonderfulis this!?!

Though I came across this emulation trick independently, I am sure it is notnovel in the Python community. I trust, however, that my example applicationof it will still be educational nonetheless.