class FooBar(models.Model):
    ...
    count = models.PositiveIntegerField()
    foo = models.CharField()
    ...


class FooBarForm(forms.ModelForm):
    def __init__(self, *args, **kwargs):
        super(FooBarForm, self).__init__(*args, **kwargs)

        # Change field meta data in a DRY way
        self.fields['count'].min_value = 1
        self.fields['count'].max_value = 30
        
        # Add html attribute in a DRY way
        self.fields['foo'].widget.attrs["size"] = 5 

    class Meta:
        model = FooBar