<SYSTEM_TASK:>
Solve the following problem using Python, implementing the functions described below, one line at a time
<END_TASK>
<USER_TASK:>
Description:
 def entity_tags_form(self, entity, ns=None):
 """Construct a form class with a field for tags in namespace `ns`."""

        if ns is None:
            ns = self.entity_default_ns(entity)

        field = TagsField(label=_l("Tags"), ns=ns)
        cls = type("EntityNSTagsForm", (_TagsForm,), {"tags": field})
        return cls