Kivy python *args

Question

ive just learn kivy, i dont understand some parameter in the caller in this tutorial :

http://pythonmobile.blogspot.com/2014/06/18-kivy-app-bezier-weight.html

i knew that *arg is the list of object which is passed into the caller. But in this function:

class Ex18(BoxLayout):
    def newWeights(self, *args):
        t = args[1]
        self.ids['w0'].value = (1-t)**3
        self.ids['w1'].value = 3*t*(1-t)**2
        self.ids['w2'].value = 3*t**2*(1-t)
        self.ids['w3'].value = t**3

What does args[1] mean ?

and this caller in KV language:

on_value: root.newWeights(*args)

what is the *arg in this caller. which parameters are passed into this, its not explicit. Hope you understand what i mean, my English isn't good. thank so much !

Answer 1

*args allows you pass an arbitrary number of arguments to your function, it is the tuple of argument that you pass to the function.

def foo(*args):
    for i in args:
        print i
    print type(args)

foo(1, 2, 3,'a')

output:-
>>> 
1
2
3
a
<type 'tuple'>

it is used when you actually don't know how many arguments are passed in the function call.

print type(args)  #<type 'tuple'>

shows you type of args

so:-

arg[0] = first element of tuple
arg[1] = second element of tuple
.
.
and so on

though it is not needed as if you know the nombers argument pass to the function call,

def foo(a, b, c, d, e):
    print a, b, c, d, e

foo(1, 2, 'this is','string', [1, 2 ,3, 4])


>>> 
1 2 this is string [1, 2, 3, 4]