Python noob's simple config problem

kj socyl at 987jk.com.invalid
Fri Jun 13 18:05:06 CEST 2008


In <g2s66c$mr$1 at kuling.itea.ntnu.no> =?iso-8859-1?q?Robin_K=E5veland?= Hansen <kaaveland at gmail.com> writes:

>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.

Thanks!

Kynn

-- 
NOTE: In my address everything before the first period is backwards;
and the last period, and everything after it, should be discarded.



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