<SYSTEM_TASK:>
Solve the following problem using Python, implementing the functions described below, one line at a time
<END_TASK>
<USER_TASK:>
Description:
 def get_or_create(cls, mp, part_number):
 """Get or create a part."""

        obj = cls.get_or_none(mp, part_number)
        if obj:
            return obj
        return cls.create(mp, part_number)