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POPython - scope of wrapping functions
 

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    <p>The goal is to wrap a function or method and carry data around with the wrapper that's unique to the wrapped function.</p> <p>As an example - let's say I have object <code>myThing</code> with method <code>foo</code>. I want to wrap <code>myThing.foo</code> with <code>myWrapper</code>, and (as an example) I want to be able to count the number of times <code>myThing.foo</code> is actually called.</p> <p>So far, the only method I've found to be effective is to just add an attribute to the object -- but this feels a little bit clumsy.</p> <pre><code>class myThing(object): def foo(self): return "Foo called." def myWrap(some_func): def _inner(self): #a wild kludge appears! try: self.count += 1 except AttributeError: self.count = 0 return some_func(self) return _inner Stick = myThing() myThing.foo = myWrap(myThing.foo) for i in range(0, 10): Stick.foo() ##outputs "Foo called." 10 times Stick.count # the value of Stick.count </code></pre> <p>So, this achieves the goal, and in fact if there are multiple instances of <code>myThing</code> then each one 'tracks' its own self.count value, which is part of my intended goal. However, I am not certain that adding an attribute to each instance of <code>myThing</code> is the best way to achieve this. If, for example, I were to write a wrapper for a function that wasn't part of an object or class, adding attributes to an object that isn't there won't do anything.</p> <p>Maybe there is a hole in my understanding of what's actually happening when a method or function is wrapped. I do know that one can maintain some kind of static data within a closure, as with the following example:</p> <pre><code>def limit(max_value): def compare(x): return x &gt; max_value return compare isOverLimit = limit(30) isOverLimit(45) #returns True isOverLimit(12) #returns False alsoOver = limit(20) alsoOver(25) # returns True isOverLimit(25) # returns False </code></pre> <p>The second example proving that it's not simply modifying the original instance of <code>limit</code>, and that <code>isOverLimit</code> continues to act as it did before the second <code>alsoOver</code> is created. So I get the sense that there's a way for the wrapper to carry an incremental variable around with it, and that I'm just missing something obvious.</p>
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