http://code.activestate.com/recipes/tags/callback/2017-04-19T18:03:11-07:00ActiveState Code Recipes2017-04-19T18:03:11-07:00Vasudev Ramhttp://code.activestate.com/recipes/users/4173351/http://code.activestate.com/recipes/580787-implementing-function-based-callbacks-in-python/

<p style="color: grey"> Python recipe 580787 by <a href="/recipes/users/4173351/">Vasudev Ram</a> (<a href="/recipes/tags/callback/">callback</a>, <a href="/recipes/tags/function/">function</a>, <a href="/recipes/tags/functions/">functions</a>, <a href="/recipes/tags/python/">python</a>, <a href="/recipes/tags/techniques/">techniques</a>). </p> <p>This recipe shows a simple way of implementing callbacks in Python. There are a few ways this can be done. The way shown here uses a simple function-based approach.</p> <p>In a nutshell, a callback can be informally described like this: function <strong>a</strong> calls function <strong>b</strong>, and wants to make <strong>b</strong> run a specific independent chunk of code at some point during <strong>b</strong>'s execution. We want to be able to vary which chunk of code gets called in different calls to <strong>b</strong>, so it cannot be hard-coded inside <strong>b</strong>. So function <strong>a</strong> passes another function, <strong>c</strong>, to <strong>b</strong>, as one argument, and <strong>b</strong> uses that parameter <strong>c</strong> to call the functionality that <strong>a</strong> wants <strong>b</strong> to call. (Function <strong>b</strong> may pass some parameters to the function represented by <strong>c</strong>, when it calls it. These could be either internally generated, passed from <strong>a</strong>, or a combination of both). So, by changing the value of the function <strong>c</strong> that gets passed to <strong>b</strong> (on different calls to <strong>b</strong>), <strong>a</strong> can change what chunk of code <strong>b</strong> calls.</p> <p>More details and full code, description and output here:</p> <p><a href="https://jugad2.blogspot.in/2017/04/implementing-and-using-callbacks-in.html" rel="nofollow">https://jugad2.blogspot.in/2017/04/implementing-and-using-callbacks-in.html</a></p>

2013-09-25T01:54:53-07:00Martin Millerhttp://code.activestate.com/recipes/users/155538/http://code.activestate.com/recipes/578674-wrap-a-a-file-like-object-in-another-that-calls-a-/

<p style="color: grey"> Python recipe 578674 by <a href="/recipes/users/155538/">Martin Miller</a> (<a href="/recipes/tags/callback/">callback</a>, <a href="/recipes/tags/file/">file</a>, <a href="/recipes/tags/oop/">oop</a>, <a href="/recipes/tags/progress/">progress</a>, <a href="/recipes/tags/upload/">upload</a>). </p> <p>Wraps a file-like object in another, but also calls a user callback with the number of bytes read whenever its <code>read()</code> method is called. Used for tracking upload progress, for example for a progress bar in a UI application.</p>

2013-09-22T21:48:03-07:00Ben Hoythttp://code.activestate.com/recipes/users/4170919/http://code.activestate.com/recipes/578669-wrap-a-string-in-a-file-like-object-that-calls-a-u/

<p style="color: grey"> Python recipe 578669 by <a href="/recipes/users/4170919/">Ben Hoyt</a> (<a href="/recipes/tags/callback/">callback</a>, <a href="/recipes/tags/file/">file</a>, <a href="/recipes/tags/progress/">progress</a>, <a href="/recipes/tags/upload/">upload</a>). </p> <p>Wraps a string in a read-only file-like object, but also calls a user callback with the number of bytes read whenever <code>read()</code> is called on the stream. Used for tracking upload progress, for example for a progress bar in a UI application.</p>