A utility class that makes writing callbacks more pleasant than using lambda. Especially using with Tkinter.
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class Command: def __init__(self, callback, *args, **kwargs): self.callback = callback self.args = args self.kwargs = kwargs def __call__(self): return apply(self.callback, self.args, self.kwargs)
(I remember seeing this utility class a while back, but don't remember who to attribute it to. Perhaps I saw this in Grayson's book.)
Writing callbacks that give customized arguments can look a little awkward with lambda, so this Command class gives an alternative syntax that's nicer. For example:
import Tkinter def hello(name): print "Hello", name root = Tk()
The lambda way of doing it:
Button(root, text="Guido", command=lambda name="Guido": hello(name)).pack()
Using the Command class:
Button(root, text="Guido", command=Command(hello, "Guido")).pack()
But what if the callback takes arguments? Your __call__ method would have to take args, *kwds arguments as well, and you'd have to merge your preset arguments and the ones given. Don't ask me how :-)
A "callback" that only supports empty argument lists isn't very useful!
tkinter often uses no args. typical tkinter callbacks have no args, so this recipe's quite useful for that need. more general curry solutions (applicable to all sort of callbacks &c) can be found in other recipes.
source of utility function. This function is definitely in Grayson's "Python and Tkinter Programming", and is credited to a Python news group posting by Timothy R. Evans.
apply(self.callback, self.args, self.kwargs)should be changed to