Why TransformListener initializiton giving an AttributeError?

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I am trying to transform a point from a map frame to camera frame. But i was getting an AttributeError. I followed this api and wrote the following code.

target = "wide_stereo_optical_frame";
point = PointStamped()
point.point.x =2;
point.point.y = 1;
point.point.z = 1;
point.header.frame_id = "map";
point.header.stamp = rospy.Time.now();                                                              tf = tf.TransformListener();                                                                        tf.waitForTransform(target, point.header.frame_id, rospy.Time(), rospy.Duration(5.0));
camera_target = tf.transformPoint(target, point)

In the above code, i was created a point in "map" frame and trying to transform into "wide_stereo_optical_frame" frame. But, I was getting an error tf.Exception: AttributeError: 'TransformListener' object has no attribute 'Exception'