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    <p>One effective way to accomplish this is to use a message-passing/communicating processes architecture, allowing you to accomplish your goal with Python, but not limiting yourself to Python.</p> <pre><code>------------------------------------ | App &lt;--&gt; Ext. API &lt;--&gt; Protocol | &lt;--&gt; (Socket) &lt;--&gt; API.py &lt;--&gt; Script ------------------------------------ </code></pre> <p>This diagram attempts to show the following: Your application communicates with external processes (for example Python) using message passing. This is efficient on a local machine, and can be portable because <em>you define your own protocol</em>. The only thing that you have to give your users is a Python library that implements your custom API, and communicates using a Send-Receive communication loop between your user's script and your application.</p> <h2>Define Your Application's External API</h2> <p>Your application's external API describes all of the functions that an external process must be able to interact with. For example, if you wish for your Python script to be able to draw a red circle in your application, your external API may include Draw(Object, Color, Position).</p> <h2>Define A Communication Protocol</h2> <p>This is the protocol that external processes use to communicate with your application through it's external API. Popular choices for this might be XML-RPC, SunRPC, JSON, or your own custom protocol and data format. The choice here needs to be sufficient for your API. For example, if you are going to be transferring binary data then JSON might require base64 encoding, while SunRPC assumes binary communication.</p> <h2>Build Your Application's Messaging System</h2> <p>This is as simple as an infinite loop receiving messages in your communication protocol, servicing the request within your application, and replying over the same socket/channel. For example, if you chose JSON then you would receive a message containing instructions to execute Draw(Object, Color, Position). After executing the request, you would reply to the request.</p> <h2>Build A Messaging Library For Python (or whatever else)</h2> <p>This is even simpler. Again, this is a loop sending and receiving messages on behalf the library user (i.e. your users writing Python scripts). The only thing this library must do is provide a programmatic interface to your Application's External API and translate requests into your communication protocol, all hidden from your users.</p> <p>Using Unix Sockets, for example, will be extremely fast.</p> <h2>Plugin/Application Rendezvous</h2> <p>A common practice for discovering application plugins is to specify a "well known" directory where plugins should be placed. This might be, for example:</p> <pre><code>~/.myapp/plugins </code></pre> <p>The next step is for your application to look into this directory for plugins that exist. Your application should have a some smarts to be able to distinguish between Python scripts that are, and are not, real scripts for your application.</p> <p>Let's assume that your communication protocol specifies that each script will communicate using JSON over StdInput/StdOuput. A simple, effective approach is to specify in your protocol that the first time a script runs it sends a MAGIC_ID to standard out. That is, your application reads the first, say, 8 bytes, and looks for a specific 64-bit value that identifies it as a script.</p> <p>Additionally, you should include in your External API methods that allow your scripts to identify themselves. For example, a script should be able to inform the application through the External API things such as <em>Name</em>, <em>Description</em>, <em>Capabilities</em>, <em>Expectations</em>, essentially informing the application what it is, and what it will be doing.</p>
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    1. POThe "right" way to add python scripting to a non-python application
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    1. COThis looks excellent, but I'm a little bit unfamiliar with this type of architecture. How would I go about "discovering" user plugins?
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    2. CO@kurige added application/plugin rendezvous suggestion.
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      1. USNoah Watkins
    3. COThis feels complicated. What is the bonus compared to other solutions that overcomes the need to write so many layers ? (except that you can extend your app with several different languages)
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