this is the code:

def create(request, form_class=MapForm, template_name="maps/create.html"):
    map_form = form_class(request.POST or None)

    if map_form.is_valid():
        map = map_form.save(commit=False)

and the map_form is :

class MapForm(forms.ModelForm):

    slug = forms.SlugField(max_length=20,
        help_text = _("a short version of the name consisting only of letters, numbers, underscores and hyphens."),
        #error_message = _("This value must contain only letters, numbers, underscores and hyphens."))
        )

    def clean_slug(self):
        if Map.objects.filter(slug__iexact=self.cleaned_data["slug"]).count() > 0:
            raise forms.ValidationError(_("A Map already exists with that slug."))
        return self.cleaned_data["slug"].lower()

    def clean_name(self):
        if Map.objects.filter(name__iexact=self.cleaned_data["name"]).count() > 0:
            raise forms.ValidationError(_("A Map already exists with that name."))
        return self.cleaned_data["name"]

    class Meta:
        model = Map
        fields = ('name', 'slug', 'description')