<SYSTEM_TASK:>
Solve the following problem using Python, implementing the functions described below, one line at a time
<END_TASK>
<USER_TASK:>
Description:
 def build_attrs(self, *args, **kwargs):
 """Add select2 data attributes."""

        attrs = super(Select2Mixin, self).build_attrs(*args, **kwargs)
        if self.is_required:
            attrs.setdefault('data-allow-clear', 'false')
        else:
            attrs.setdefault('data-allow-clear', 'true')
            attrs.setdefault('data-placeholder', '')

        attrs.setdefault('data-minimum-input-length', 0)
        if 'class' in attrs:
            attrs['class'] += ' django-select2'
        else:
            attrs['class'] = 'django-select2'
        return attrs