http://code.activestate.com/recipes/tags/callback-progress/top/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>