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POOO design: an object that can be exported to a "row", while accessing header names, without repeating myself
 

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  1. POOO design: an object that can be exported to a "row", while accessing header names, without repeating myself
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    <p>Sorry, badly worded title. I hope a simple example will make it clear. Here's the easiest way to do what I want to do:</p> <pre><code>class Lemon(object): headers = ['ripeness', 'colour', 'juiciness', 'seeds?'] def to_row(self): return [self.ripeness, self.colour, self.juiciness, self.seeds &gt; 0] def save_lemons(lemonset): f = open('lemons.csv', 'w') out = csv.writer(f) out.write(Lemon.headers) for lemon in lemonset: out.writerow(lemon.to_row()) </code></pre> <p>This works alright for this small example, but I feel like I'm "repeating myself" in the Lemon class. And in the actual code I'm trying to write (where the number of variables I'm exporting is ~50 rather than 4, and where to_row calls a number of private methods that do a bunch of weird calculations), it becomes awkward. </p> <p>As I write the code to generate a row, I need to constantly refer to the "headers" variable to make sure I'm building my list in the correct order. If I want to change the variables being outputted, I need to make sure to_row and headers are being changed in parallel (exactly the kind of thing that DRY is meant to prevent, right?).</p> <p>Is there a better way I could design this code? I've been playing with function decorators, but nothing has stuck. Ideally I should still be able to get at the headers without having a particular lemon instance (i.e. it should be a class variable or class method), and I don't want to have a separate method for each variable.</p>
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    1. COthe `?` in the seeds attribute is awfully peculiar, and makes a number of python idioms (`collections.namedtuple`, `property` come to mind) which would otherwise improve your situation, awkward or otherwise violate DRY principles. How important is that?
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    2. CONot especially important in my particular case. Of course, I'd prefer a solution that's amenable to headers that include spaces and special characters, since that would be more generally applicable. BTW using properties is not desirable since I don't want to have one method for each variable (some groups of variables need to be calculated simultaneously for efficiency, and I don't want to juggle shared state with extra instance variables).
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    3. CODo you actually have code that accesses a `lemon.ripeness` anywhere, or only code that deals with lemons as rows, etc.? If the latter, why not just store a `dict` mapping headers to values, and not bother trying to make those values accessible as attributes? (And if the former, you're not going to be able to write `lemon.seeds?` anywhere…)
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