Django 1.2 UUIDField with South support

from django.db import models

import uuid

class UUIDField(models.CharField):
    """
    A field which stores a UUID value in hex format. This may also have                     
    the Boolean attribute 'auto' which will set the value on initial save to a              
    new UUID value (calculated using the UUID1 method). Note that while all                 
    UUIDs are expected to be unique we enforce this with a DB constraint.                   
    """                                                                                     
    # Modified from http://www.davidcramer.net/code/420/improved-uuidfield-in-django.html   
    __metaclass__ = models.SubfieldBase                                                     
                                                                                            
    def __init__(self, auto=False, *args, **kwargs):                                        
        if kwargs.get('primary_key', False):                                                
            assert auto, "Must pass auto=True when using UUIDField as primary key."         
        self.auto = auto                                                                    
        # Set this as a fixed value, we store UUIDs in text.                                
        kwargs['max_length'] = 32                                                           
        if auto:                                                                            
            # Do not let the user edit UUIDs if they are auto-assigned.                     
            kwargs['editable'] = False                                                      
            kwargs['blank'] = True                                                          
            kwargs['unique'] = True                                                         
        super(UUIDField, self).__init__(*args, **kwargs)                                    
                                                                                            
    def db_type(self):                                                                      
        return 'uuid'                                                                       
                                                                                            
    def pre_save(self, model_instance, add):                                                
        """Ensures that we auto-set values if required. See CharField.pre_save."""          
        value = getattr(model_instance, self.attname, None)                                 
        if not value and self.auto:                                                         
            # Assign a new value for this attribute if required.                            
            value = uuid.uuid4().hex                                                        
            setattr(model_instance, self.attname, value)                                    
        return value

    def to_python(self, value):                                                          
        if not value:
            return None
        if len(value) != 32:
            value = value.replace('-', '')                                               
        assert len(value) == 32                                                          
        return value                                                              

    def south_field_triple(self):
        "Returns a suitable description of this field for South."
        # We'll just introspect the _actual_ field.
        from south.modelsinspector import introspector
        field_class = "django.db.models.fields.CharField"
        args, kwargs = introspector(self)
        # That's our definition!
        return (field_class, args, kwargs)