Python noob's simple config problem

Robin Kåveland Hansen kaaveland at gmail.com
Thu Jun 12 23:58:36 CEST 2008


On Thu, 12 Jun 2008 21:32:34 +0000, kj wrote:

> I'm sure this is a simple, but recurrent, problem for which I can't hit
> on a totally satisfactory solution.
> 
> As an example, suppose that I want write a module X that performs some
> database access.  I expect that 99.999% of the time, during the
> foreseeable future, the database connection parameters will remain
> unchanged.  The only exception that I envision for this would be during
> testing or debugging.
> 
> Given all this, I am tempted to turn these connection parameters into
> hard-coded module attributes that I can always override (i.e. overwrite)
> when necessary.
> 
> But for as long as I can remember the dogma has been that hard-coded
> values are bad, and that one should use other techniques, such as
> configuration files, or parameters to a suitable constructor, etc.
> 
> This is where I begin to get confused: whose responsibility is it to
> know of and read the config file?  I can think of two distinct
> scenarios: 1) module X is being used by a large, full-fledged
> application A that already uses a config file for its own configuration;
> 2) module X is being used by a simple script that has no need for a
> config file.  In case 1 I'd be glad to let application A set module X's
> connection parameters using values read from its own (i.e. A's) config
> file; this minimizes the number of config files that need to be
> maintained.  In case 2, however, it would be preferable for module X to
> read its connection params from its own (i.e. X's) config file.  In this
> way the script won't have to bother setting some parameters that are in
> fact practically constant...
> 
> After going round and round on this, my original idea of hard-coding the
> values as module attributes begins to look pretty attractive again.
> 
> How would you handle such situations?
> 
> Thanks!
> 
> kynn

I think I would just abstract it away with a "getter" for the connection, 
a function that takes some optional parameters, if not supplied, it 
simply fetches them from a default configuration. Ie:

def connect(params=None):
    if params is None:
        return dblayer.connect(conf["default"])
    else:
        return dblayer.connect(params)

Unless I have misunderstood you completely? Now people can change your 
scripts config file, and if someone wants to use your code, they can use 
the getter directly.

I hope this is of some help.



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