Question about code writing '% i, callback'

[Ian Kelly]

On Mon, Nov 30, 2015 at 10:44 AM, fl <rxjwg98 at gmail.com> wrote:
> I come across the following code snippet.
>
> for i in range(10):
>     def callback():
>         print "clicked button", i
>     UI.Button("button %s" % i, callback)
>
> The content inside parenthesis in last line is strange to me.
>
> "button %s" % i, callback

These are the arguments being passed to UI.Button. The first argument is:

    "button %s" % i

This is an example of printf-style string formatting. See the link
that Zachary posted.

The second argument is the function named callback.

> That is, the writing looks like recognized as three items when I try with a
> class definition (it can run with this):
>
> class buibutton():
>     print 'sd'
>     def __nonzero__(self):
>        return False
>
>     def Button(str, ii, callbackk):
>
>         return
>
>
> Could you explain it to me?

How is this related to the example above?

Here, Button is defined as a method of a class. Since it's a method,
the first parameter is the "self" parameter, which will implicitly
take the value of the class instance that you're calling the Button
method on. If you're trying to call this like above, then the second
parameter "ii" will take the value of the string from the example
above, and callbackk will take the value of the callback argument from
above.

Thus, the method that you've defined has three parameters but only
takes two explicit arguments.