Where to set default data - where received, or where used

[Nick Cash]

This is really up to your programming style, but I'm of the opinion that defining all of the default values in one place keeps maintenance easier.

Of course, if it's done differently elsewhere in your code base, I would aim for consistency instead.

Thanks,
Nick Cash

-----Original Message-----
From: python-list-bounces+nick.cash=npcinternational.com at python.org [mailto:python-list-bounces+nick.cash=npcinternational.com at python.org] On Behalf Of Dennis Carachiola
Sent: Monday, June 11, 2012 13:38
To: python-list at python.org
Subject: Where to set default data - where received, or where used

I'm programming a project which will use a file to save parameters needed by the program.  There are already two previous file formats, each of which can only be run by the version of the program which created them.  I'm trying to avoid that problem in the future.  To do that, I intend to use a dictionary, and default data.  I believe that most new versions will add parameters.

Each version of the program will have reasonable default values for each key in the dictionary handled by that version.  If an older file is used, the data values in that file replace the keys that exist.
The program then can operate on the values supplied by the older data file and the default values.  Conversely, if a newer file is used, the data in the file replaces the keys in the dictionary.  The program then simply doesn't access the newer data values.  I'm hoping that this will make the file backward and forward compatible.

Here's my question.  I could do this by creating the dictionary with the default values, then read the file into it.  Or I could use a 'get' with default values at the location in the program where those values are used.

>From what I can see, creating the dictionary with default values puts
everything in one place.  While, supplying the default values at the place where they're used places the default values nearest the place where actually used.

I can't decide on one way over the other.  Can anyone give me some ideas if one is a preferred method, or other criteria I've overlooked?

Thanks,

Den
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