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PORecipe for anonymous functions in python?
 

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  1. PORecipe for anonymous functions in python?
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    <p>I'm looking for the best recipie to allow inline definition of functions, or multi-line lambda, in python.</p> <p>For example, I'd like to do the following:</p> <pre><code>def callfunc(func): func("Hello") &gt;&gt;&gt; callfunc(define('x', ''' ... print x, "World!" ... ''')) Hello World! </code></pre> <p>I've found an example for the <code>define</code> function in <a href="https://stackoverflow.com/a/6630330/143091">this answer</a>:</p> <pre><code>def define(arglist, body): g = {} exec("def anonfunc({0}):\n{1}".format( arglist, "\n".join(" {0}".format(line) for line in body.splitlines())), g) return g["anonfunc"] </code></pre> <p>This is one possible solution, but it is not ideal. Desireable features would be:</p> <ul> <li>be smarter about indentation,</li> <li>hide the innards better (e.g. don't have <code>anonfunc</code> in the function's scope)</li> <li>provide access to variables in the surrounding scope / captures</li> <li>better error handling</li> </ul> <p>and some things I haven't thought of. I had a really nice implementation once that did most of the above, but I lost in unfortunately. I'm wondering if someone else has made something similar.</p> <h2>Disclaimer:</h2> <p>I'm well aware this is controversial among Python users, and regarded as a hack or unpythonic. I'm also aware of the discussions regaring multi-line-lambdas on the python-dev mailing list, and that a similar feature was omitted on purpose. However, from the same discussions I've learned that there is also interest in such a function by many others.</p> <p><strong>I'm not asking whether this is a good idea or not</strong>, but instead: <strong>Given that one has decided to implement this</strong>, (either out of fun and curiosity, madness, genuinely thinking this is a nice idea, or being held at gunpoint) <strong>how to make anonymous <code>define</code> work as close as possible to <code>def</code> using python's (2.7 or 3.x) current facilities?</strong></p> <h2>Examples:</h2> <p>A bit more as to why, this can be really handy for callbacks in GUIs:</p> <pre><code># gtk example: self.ntimes = 0 button.connect('clicked', define('*a', ''' self.ntimes += 1 label.set_text("Button has been clicked %d times" % self.ntimes) ''') </code></pre> <p>The benefit over defining a function with <code>def</code> is that your code is in a more logical order. This is simplified code taken from a Twisted application:</p> <pre><code># twisted example: def sayHello(self): d = self.callRemote(HelloCommand) def handle_response(response): # do something, this happens after (x)! pass d.addCallback(handle_response) # (x) </code></pre> <p>Note how it seems out of order. I usually break stuff like this up, to keep the code order == execution order:</p> <pre><code>def sayHello_d(self): d = self.callRemote(HelloCommand) d.addCallback(self._sayHello_2) return d def _sayHello_2(self, response): # handle response pass </code></pre> <p>This is better wrt. ordering but more verbose. Now, with the anonymous functions trick:</p> <pre><code>d = self.callRemote(HelloCommand) d.addCallback(define('response', ''' print "callback" print "got response from", response["name"] ''')) </code></pre>
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    1. COIck! Just define a normal function; this makes debugging so much the harder.
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    2. COI vehemently detest this.
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    3. COYou'd better use callbacks and/or decorator rather than python code in strings.
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