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Solve the following problem using Python, implementing the functions described below, one line at a time
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Description:
 def build(self):
 """Builds a Solenoid using the defined attributes."""

        self._molecules = []
        if self.handedness == 'l':
            handedness = -1
        else:
            handedness = 1
        rot_ang = self.rot_ang * handedness
        for i in range(self.num_of_repeats):
            dup_unit = copy.deepcopy(self.repeat_unit)
            z = (self.rise * i) * numpy.array([0, 0, 1])
            dup_unit.translate(z)
            dup_unit.rotate(rot_ang * i, [0, 0, 1])
            self.extend(dup_unit)
        self.relabel_all()
        return