<SYSTEM_TASK:>
Solve the following problem using Python, implementing the functions described below, one line at a time
<END_TASK>
<USER_TASK:>
Description:
 def rename_axis(self, mapper, axis, copy=True, level=None):
 """ Rename one of axes. Parameters mapper : unary callable axis : int copy : boolean, default True level : int, default None """

        obj = self.copy(deep=copy)
        obj.set_axis(axis, _transform_index(self.axes[axis], mapper, level))
        return obj