<SYSTEM_TASK:>
Solve the following problem using Python, implementing the functions described below, one line at a time
<END_TASK>
<USER_TASK:>
Description:
 def list_names(cls):
 """Retrieve paas id and names."""

        ret = dict([(item['id'], item['name'])
                    for item in cls.list({'items_per_page': 500})])
        return ret