[Tutor] Callbacks in Python

[Jramak]

Thanks everyone for your excellent insights. I think I understand the
callback concept better.
So, it is like passing a function as an argument to another function.
I am interested in learning more about how callbacks can be applied in
GUIs, using  wxPython as an example. Would appreciate any insight.

Thanks much
Jramak

On 8/27/09, Alan Gauld <alan.gauld at btinternet.com> wrote:
>
> "Jramak" <jramak345 at gmail.com> wrote
>
>> I'm confused by callbacks. I would really appreciate any introduction or
>> help in understanding the concept of callbacks.
>
> Callbacks are used in all sorts of different ways in programming
> so it might help to undertand what exactly confuses you.
>
> Is it the whole concept of a callback?
> Is it the idea of a function as an object?
> Is it the use of callbacks?
>     In a GUI? In a networking framework like Twisted?
>
> Do you want to use someone elses callback mechanism
> or do you want to create your own?
>
> The basic name comnes from  the concept of calling
> someone, asking them to do someting then call you back
> when they are done. So you leave your number with them.
> The number you leave is what they "call back".
> In programming you call a function and at some critical
> point that function calls you back on the function that
> you passed in.
>
> def someFunction(value, callback)
>        result = pow(value,2)
>        callback(result)
>
> def myFunction()
>        v = 42
>        someFunction(v, myFunction_continue)
>
> def myFunction_contiinue(result)
>       print result
>
> myFunction()
>
> This was very useful before threading environments became
> common as a way of simulating multi threading. Then when GUIs
> came along it bacame a common way of associating functions
> with widgets. And in networking we can associate network events
> with functions in a similar way. In fact any kind of event driven
> program is likely to use callbacks as a way of distributing control
> depending on event type. The typical implementation will see the
> event framework storing the callbacks in some kind of dictionary
> keyed by event type.
>
> HTH,
>
>
> --
> Alan Gauld
> Author of the Learn to Program web site
> http://www.alan-g.me.uk/
>
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