os.path.walk arg

[Erik Max Francis]

Tim Peters wrote:

> [Afanasiy]
>
> > What is the purpose of arg in os.path.walk(path, visit, arg) ?
> 
> It's just something passed to every visit() call.  Passing None is
> fine.  So
> is passing 42.  You can do something useful with it by passing a
> mutable
> object, and writing your visit() function to mutate that object.  For
> example, you can arrange to have your visit() function accumulate a
> list of
> all .py files it found.  Or you can use it to pass in control
> information,
> such as a list of file extensions you want to ignore.

This is, by the way, a pretty standard mechanism used in APIs that
support callbacks; you give a callback, and an object/pointer/reference
that will be sent to the callback by the caller, so that one can create
a context for the callback.  (I know Tim knows this; this is for
Afanasiy's benefit.)

-- 
 Erik Max Francis / max at alcyone.com / http://www.alcyone.com/max/
 __ San Jose, CA, USA / 37 20 N 121 53 W / &tSftDotIotE
/  \ If I had known, I would have become a watchmaker.
\__/ Albert Einstein
    Bosskey.net / http://www.bosskey.net/
 A personal guide to online multiplayer first person shooters.