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POpython: How do I dynamically create bound methods from user supplied source code?
 

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  1. POpython: How do I dynamically create bound methods from user supplied source code?
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    <p>I would like to construct a class in python that supports dynamic updating of methods from user supplied source code.</p> <p>Instances of class <code>Agent</code> have a method <code>go</code>. At the time an instance is constructed, its <code>.go()</code> method does nothing. For example, if we do <code>a=Agent()</code>, and then <code>a.go()</code> we should get a <code>NotImplementedError</code> or something like that. The user then should be able to interactively define <code>a.go()</code> by supplying source code. A simple source code example would be</p> <p>mySourceString = <code>"print('I learned how to go!')"</code></p> <p>which would be injected into <code>a</code> like this <code>a.update(mySourceString)</code></p> <p>Further invokations of <code>a.go()</code> would then result in <code>"I learned how to go!"</code> being printed to the screen.</p> <p>I have partially figured out how to do this with the following code:</p> <pre><code>import types class Error(Exception): """Base class for exceptions in this module.""" pass class NotImplementedError(Error): pass class Agent(object): def go(self): raise NotImplementedError() def update(self,codeString): #Indent each line of user supplied code codeString = codeString.replace('\n','\n ') #Turn code into a function called func exec "def func(self):\n"+' '+codeString #Make func a bound method on this instance self.go = types.MethodType(func, self) </code></pre> <p>QUESTIONS</p> <ol> <li>Is this implementation sensible?</li> <li>Will this implementation incur unexpected scope issues?</li> <li>Is there an obvious way to sandbox the user supplied code to prevent it from touching external objects? I can think of ways to do this by supplying sets of allowed external objects, but this seems not pythonic.</li> </ol> <p>Possibly useful SO posts</p> <ol> <li><a href="https://stackoverflow.com/questions/2220699/whats-the-difference-between-eval-exec-and-compile-in-python">What's the difference between eval, exec, and compile in Python?</a></li> <li><a href="https://stackoverflow.com/questions/972/adding-a-method-to-an-existing-object">Adding a Method to an Existing Object</a></li> </ol> <p>(I am working in python 2.6)</p>
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    1. USMartinis Group
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    1. COCan't the go method just delegate to a hidden internal method?
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      1. POpython: How do I dynamically create bound methods from user supplied source code?
      1. USEric
    2. COSure but the whole game is to dynamically construct that method from user provided source...
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      1. POpython: How do I dynamically create bound methods from user supplied source code?
      1. USMartinis Group
    3. COMy point is that it might be beneficial to add a layer of indirection, and swap out the source of the layer below. That way, if I make a reference to `Agent.go` somewhere in my code (`foo = Agent.go`), then it will still call the most recent code from the user when I call foo at a later date.
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      1. POpython: How do I dynamically create bound methods from user supplied source code?
      1. USEric
 

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