The tf prefix is a parameter that determines the prefix that will go before the name of a tf frame from broadcasters such as gazebo and the robot state publisher, similar to namespacing with nodes that publish to topics. It is important to include
inside the namespace spawning the robots.
However, not everything uses tf_prefix as it is deprecated in tf2. In most cases, the tf prefix will likely remain the same as the namespace in order to be compatible with most packages that rely on topics and tf trees, such as gmapping, which disregard the use of tf prefixes and use namespace for tf frames.
To retrieve the current namespace with rospy, use rospy.get_namespace(). This will return the namespace with / before and after the name. To remove the /s, use rospy.get_namespace()[1:-1].