(Psutil) speed net, mtu and isup don't change automatically

Question

When I run the script, speed, mtu and isup doesn't change automatically. Only if I finish the process and start another time.

import psutil
import time
import os

stats = psutil.net_if_stats()

while True:
    time.sleep(1)
    os.system("clear")
  for nic, addrs in psutil.net_if_addrs().items():
            print("%s:" % (nic))
            if nic in stats:
                st = stats[nic]
                print("    stats          : ", end='')
                print("speed=%sMB, mtu=%s, up=%s" % (
                    st.speed, st.mtu,
                    "yes" if st.isup else "no"))

I tried to get speed, mtu and isup of each addresses associated to each NIC (network interface card) and changing in this repeat loop, but it doesn't works like this.