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Newsgroups: comp.lang.python
Date: Sun, 9 Dec 2012 17:34:16 -0800 (PST)
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Subject: Re: Creating different classes dynamically?
From: Victor Hooi <victorhooi@gmail.com>
To: comp.lang.python@googlegroups.com
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Cc: Victor Hooi <victorhooi@gmail.com>, d@davea.name, python-list@python.org
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Xref: csiph.com comp.lang.python:34536

heya,

Dave: Ahah, thanks =).

You're right, my terminology was off, I want to dynamically *instantiate*, not create new classes.

And yes, removing the brackets worked =).

Cheers,
Victor

On Monday, 10 December 2012 11:53:30 UTC+11, Dave Angel  wrote:
> On 12/09/2012 07:35 PM, Victor Hooi wrote:
> 
> > Hi,
> 
> >
> 
> > I have a directory tree with various XML configuration files.
> 
> >
> 
> > I then have separate classes for each type, which all inherit from a base. E.g.
> 
> >
> 
> >     class AnimalConfigurationParser:
> 
> >         ...
> 
> >
> 
> >     class DogConfigurationParser(AnimalConfigurationParser):
> 
> >         ...
> 
> >
> 
> >     class CatConfigurationParser(AnimalConfigurationParser):
> 
> >         ....
> 
> >
> 
> > I can identify the type of configuration file from the root XML tag.
> 
> >
> 
> > I'd like to walk through the directory tree, and create different objects based on the type of configuration file:
> 
> >
> 
> >     for root, dirs, files in os.walk('./'):
> 
> >         for file in files:
> 
> >             if file.startswith('ml') and file.endswith('.xml') and 'entity' not in file:
> 
> >                 with open(os.path.join(root, file), 'r') as f:
> 
> >                     try:
> 
> >                         tree = etree.parse(f)
> 
> >                         root = tree.getroot()
> 
> >                         print(f.name)
> 
> >                         print(root.tag)
> 
> >                         # Do something to create the appropriate type of parser
> 
> >                     except xml.parsers.expat.ExpatError as e:
> 
> >                         print('Unable to parse file {0} - {1}'.format(f.name, e.message))
> 
> >
> 
> > I have a dict with the root tags - I was thinking of mapping these directly to the functions - however, I'm not sure if that's the right way to do it? Is there a more Pythonic way of doing this?
> 
> >
> 
> >     root_tags = {
> 
> >                    'DogRootTag': DogConfigurationParser(),
> 
> >                     'CatRootTag': CatConfigurationParser(),
> 
> >     }
> 
> >
> 
> > Cheers,
> 
> > Victor
> 
> 
> 
> Your subject line says you want to create the classes dynamically, but
> 
> that's not what your code implies.  if you just want to decide which
> 
> class to INSTANTIATE dynamically, that's easily done, and you have it
> 
> almost right.  In your dict you should leave off those parentheses.
> 
> 
> 
> 
> 
> 
> 
> Then the parser creation looks something like:
> 
>                parser_instance = root_tags[root.tag] (arg1, arg2)
> 
> 
> 
> where the arg1, arg2 are whatever arguments the __init__ of these
> 
> classes expects.
> 
> 
> 
> (untested)
> 
> 
> 
> -- 
> 
> 
> 
> DaveA