South's freeze_apps

gistfile1.py

def freeze_apps(apps):
    """
    Takes a list of app labels, and returns a string of their frozen form.
    """
    if isinstance(apps, basestring): # @kenny: checks that the passed in arg is str/unicode 
        apps = [apps] # if 'apps' is a str/unicode, convert to list
    frozen_models = set()
    # For each app, add in all its models
    for app in apps:
        for model in models.get_models(models.get_app(app)):
        # @kenny: where the magic happens, see blog post further down :)
            # Only add if it's not abstract or proxy
            if not model._meta.abstract and not getattr(model._meta, "proxy", False):
                frozen_models.add(model)
    # Now, add all the dependencies
    for model in list(frozen_models):
        frozen_models.update(model_dependencies(model))
    # Serialise!
    model_defs = {} # @kenny: the hot sauce - dictionary of dictionaries containing dictionary of the field names as key, and a tuple (fields info) 
    model_classes = {}
    for model in frozen_models:
        model_defs[model_key(model)] = prep_for_freeze(model)
        model_classes[model_key(model)] = model
    # Check for any custom fields that failed to freeze.
    missing_fields = False
    for key, fields in model_defs.items():
        for field_name, value in fields.items():
            if value is None:
                missing_fields = True
                model_class = model_classes[key]
                field_class = model_class._meta.get_field_by_name(field_name)[0]
                print " ! Cannot freeze field '%s.%s'" % (key, field_name)
                print " ! (this field has class %s.%s)" % (field_class.__class__.__module__, field_class.__class__.__name__)
    if missing_fields:
        print ""
        print " ! South cannot introspect some fields; this is probably because they are custom"
        print " ! fields. If they worked in 0.6 or below, this is because we have removed the"
        print " ! models parser (it often broke things)."
        print " ! To fix this, read http://south.aeracode.org/wiki/MyFieldsDontWork"
        sys.exit(1)
    
    return model_defs