New configuration module - interfacing to command line options

[Vinay Sajip]

Neal,
> 
> I believe a decent config module should at least handle both config files
> and command line options.  ENV variables are a nice touch too.
> 
Further to my earlier post, I did a bit of thinking and find it very 
easy to accommodate command line options read via optparse within the 
overall configuration framework. Consider the following hypothetical 
configuration file 'cmdline.cfg':

cmdline_values:
{
   verbose : `cmdline.verbose`
   file: `cmdline.filename`
}
other_config_items:
{
   whatever : 'you want'
}

The values of interest are those provided in the 'cmdline_values' part 
of the configuration. (You can, of course, use whatever structure you 
like - this is only an example.)

Consider the following program:

from optparse import OptionParser
from config import Config

parser = OptionParser()
parser.add_option("-f", "--file",
                 action="store", type="string", dest="filename",
                 help="write report to FILE", metavar="FILE")
parser.add_option("-q", "--quiet",
                 action="store_false", dest="verbose", default=1,
                 help="don't print status messages to stdout")

(options, args) = parser.parse_args()

cfg = Config(file('cmdline.cfg'))
cfg.addNamespace(options, 'cmdline')
print "The verbose option value is %r" % cfg.cmdline_values.verbose
print "The file name is %r" %  cfg.cmdline_values.file

After parsing the command line using OptionParser, we read in the 
configuration (possibly getting the configuration file from the parsed 
options, though not in this case). We also add a namespace called 
'cmdline' which adds the parsed option settings to the configuration. 
When we later reference cfg.cmdline_values.verbose, this references 
`cmdline.verbose`, and this resolves to the 'verbose' attribute of the 
parsed-options object (added under the name 'cmdline'). The program will 
print

The verbose option value is False
The file name is 'test'

as you would expect.

N.B. I had to make a small change to the Config.addNamespace method to 
get this to work. The current release (0.3) does not have this fix, but 
the next release will.

Best regards,



Vinay Sajip