About my confusion about ip-routing demo

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Much thanks for reading this.I'm really looking forward to your reply!
I'm trying to learn p4 program,and I suppose I understand the basic things of p4. When I analyze your ip-routing in p4-demo,I can understand the p4 program,but I don't quite understand the topo.py,that is,why sw_path or json_path is needed,or what does this mean?

s1 = self.addSwitch('s1',
                            sw_path=sw_path,
                            json_path=json_path,
                            thrift_port=9090)
s2 = self.addSwitch('s2',
                            sw_path=sw_path,
                            json_path=json_path,
                            thrift_port=9091)
 s3 = self.addSwitch('s3',
                            sw_path=sw_path,
                            json_path=json_path,
                            thrift_port=9092)

so I change the program,without the sw_path,json_path in the addSwitch:

import sys
sys.path.append('../')
sys.path.append('/home/p4/tutorials/utils')
from p4_mininet import P4Switch, P4Host
from mininet.topo import Topo
from mininet.net import Mininet
from mininet.log import setLogLevel, info
from mininet.cli import CLI

import argparse



class DemoTopo(Topo):
    "Demo topology"

    def __init__(self,**opts):
        # Initialize topology and default options
        Topo.__init__(self, **opts)

        s1 = self.addSwitch('s1',
                            thrift_port=9090)
        s2 = self.addSwitch('s2',
                            thrift_port=9091)
        s3 = self.addSwitch('s3',
                            thrift_port=9092)

        h1 = self.addHost('h1',
                            ip="10.0.10.10/24",
                            mac='00:00:00:00:00:01')
        h2 = self.addHost('h2',
                          ip="10.0.20.10/24",
                          mac='00:00:00:00:00:02')
        h3 = self.addHost('h3',
                          ip="10.0.30.10/24",
                          mac='00:00:00:00:00:03')

        self.addLink(s1, h1)
        self.addLink(s2, h2)
        self.addLink(s3, h3)

        self.addLink(s1, s2)
        self.addLink(s2, s3)
        self.addLink(s1, s3)


def main():
    topo = DemoTopo()

    net = Mininet(topo=topo,
                  host=P4Host,
                  switch=P4Switch,
                  controller=None)
    net.start()

    s1 = net.get('s1')
    s1.setIP('10.0.10.1/24', intf = 's1-eth1')
    s1.setMAC('00:00:00:00:01:01', intf = 's1-eth1')
    s1.setIP('192.168.1.1/24', intf = 's1-eth2')
    s1.setMAC('00:00:00:00:01:02', intf='s1-eth2')
    s1.setIP('192.168.3.254/254', intf = 's1-eth3')
    s1.setMAC('00:00:00:00:01:03', intf='s1-eth3')

    s2 = net.get('s2')
    s2.setIP('10.0.20.1/24', intf = 's2-eth1')
    s2.setMAC('00:00:00:00:02:01', intf='s2-eth1')
    s2.setIP('192.168.3.1/24', intf = 's2-eth2')
    s2.setMAC('00:00:00:00:02:02', intf='s2-eth2')
    s2.setIP('192.168.2.254/24', intf = 's2-eth3')
    s2.setMAC('00:00:00:00:02:03', intf='s2-eth3')

    s3 = net.get('s3')
    s3.setIP('10.0.30.1/24', intf='s3-eth1')
    s3.setMAC('00:00:00:00:03:01', intf='s3-eth1')
    s3.setIP('192.168.2.1', intf='s3-eth2')
    s3.setMAC('00:00:00:00:03:02', intf='s3-eth2')
    s3.setIP('192.168.1.254/24', intf='s3-eth3')
    s3.setMAC('00:00:00:00:03:03', intf='s3-eth3')

    h1 = net.get('h1')
    h1.setDefaultRoute("dev eth0 via 10.0.10.1")

    h2 = net.get('h2')
    h2.setDefaultRoute("dev eth0 via 10.0.20.1")

    h3 = net.get('h3')
    h3.setDefaultRoute("dev eth0 via 10.0.30.1")

    print("Ready !")

    CLI(net)

    net.stop()

if __name__ == '__main__':
    setLogLevel('info')
    main()

But when I run the code,the compiler told me this:

In fact,I just want to implement the ip routing in p4,and I want to specify the ip address for the p4 switch.Therefore,I have such confusion.