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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 set_obs_angle(self, theta_rad):
 """Set the observer angle relative to the field. **Call signature** *theta_rad* The angle between the ray path and the local magnetic field, in radians. Returns *self* for convenience in chaining. """

        self.in_vals[IN_VAL_THETA] = theta_rad * 180 / np.pi # rad => deg
        return self