New configuration module released

[Dan Perl]

Vinay,

I'm posting some opinions I have on your module and on the topic in general 
in this newsgroup, instead of using the links you have on your web page 
(your email and a wiki) because I would like to see a wider discussion.

My experience with python in general and configuration in python in 
particular is rather short (a few months), but I have been working on a 
personal, open-source project during this time and configuration was one of 
the biggest issues I had.  I did look at configParser early on, but I 
decided it was not giving me enough.  At the top level, I had only a few 
values (4 at present, but even less in the beginning) and these values were 
however fairly complex.  I ended up implementing the configuration mechanism 
as plain python modules which are imported by my application.  This created 
a mechanism that was relatively difficult to understand and that needed 
users to actually code in python for configuration.  I think the problem of 
configuration in my project is much smaller now, because I also added a GUI 
tool that allows configuration to be done through a graphical interface.

Enough about my project, but I meant to give a context for what I am about 
to discuss next.

I looked only at the documentation for your module and I haven't actually 
tried it.  Please forgive me if I am missing anything.  With this 
information though, I don't see enough reasons to replace my own custom-made 
configuration mechanism with your module.

First, some small issues.  The syntax for your configuration is still fairly 
close to the python syntax and it involves quite a bit of learning for both 
python users and non-python users.  Your module would save me a little bit 
of work in parsing when loading a configuration (remember, I am loading 
configurations by importing them as a module) and a little more work than 
that in formatting when saving a configuration.  That work is not very 
significant though and having my own mechanism also has its advantages.

Now, here is the biggest issue I have and what I would be extremely 
interested in seeing in a configuration module.  I don't see from your 
documentation how I could programmatically create a configuration from 
scratch.  In my project I have a set of handlers and each handler has a 
special configuration.  Each such special configuration is defined by a 
structure of metadata (with information like name, type, description) that I 
implemented myself.  That way, my GUI tool can load a handler dynamically, 
read its configuration metadata, dynamically create a frame for the 
handler's configuration, and save the new configuration to a file.

Again, I only read your documentation, but I haven't seen anything like my 
configuration metadata, that would allow me to dynamically create a 
configuration from scratch.  Please correct me if I'm wrong and point me to 
something that your module has for this purpose.

I definitely appreciate your effort though and I hope that you continue 
working on this configuration module.  Like I said, configuration has been a 
big issue in my project and I would like to have a generic configuration 
that would satisfy all my needs instead of creating (and now evolving and 
maintaining) my own, custom-made configuration mechanism.  Something like 
the configuration metadata that I described is a very important feature for 
me.  I hope I described it clearly enough.  And again, my apologies if you 
already have such a feature and I only missed it.

Dan

"Vinay Sajip" <vinay_sajip at yahoo.co.uk> wrote in message 
news:2e37dc1.0411030650.ff44840 at posting.google.com...
> I've just made available the first general release of a configuration
> module for Python. It has grown out of the need to make configuration
> easier and more powerful (for developers and end users) than
> ConfigParser.
>
> It's one of the implementations which could be considered in the
> ConfigParser shootout, mentioned on the Python Wiki at
>
> http://www.python.org/moin/ConfigParserShootout
>
> What Does It Do?
> ================
> The config module allows you to implement a hierarchical configuration
> scheme with support for mappings and sequences, cross-references
> between one part of the configuration and another, the ability to
> flexibly access real Python objects, facilities for configurations to
> include and cross-reference one another, simple expression evaluation
> and the ability to change, save, cascade and merge configurations.
>
> This module has been developed on python 2.3 but should work on
> version 2.2 or greater. A test suite using unittest is included in the
> distribution.
>
> A very simple configuration file (simple.cfg):
>
> # starts here
> message: Hello, world!
> #ends here
>
> a very simple program to use it:
>
> from config import Config
>
> cfg = Config(file('simple.cfg'))
> print cfg.message
>
> results in:
>
> Hello, world!
>
> Configuration files are key-value pairs, but the values can be
> containers that contain further values
> A simple example - with the example configuration file:
>
> messages:
> [
>  {
>    stream : `sys.stderr`
>    message: 'Welcome'
>    name: 'Harry'
>  }
>  {
>    stream : `sys.stdout`
>    message: 'Welkom'
>    name: 'Ruud'
>  }
>  {
>    stream : $messages[0].stream
>    message: 'Bienvenue'
>    name: Yves
>  }
> ]
>
> a program to read the configuration would be:
>
> from config import Config
>
> f = file('simple.cfg')
> cfg = Config(f)
> for m in cfg.messages:
>    s = '%s, %s' % (m.message, m.name)
>    try:
>        print >> m.stream, s
>    except IOError, e:
>        print e
>
> which, when run, would yield the console output:
>
> Welcome, Harry
> Welkom, Ruud
> Bienvenue, Yves
>
> The above example just scratches the surface. There's more information
> about this module available at
>
> http://www.red-dove.com/python_config.html
>
> Comprehensive API documentation is available at
>
> http://www.red-dove.com/config/index.html
>
> As always, your feedback is most welcome (especially bug reports,
> patches and suggestions for improvement). Enjoy!
>
> Cheers
>
> Vinay Sajip
> Red Dove Consultants Ltd.