diff --git a/tests/scripts/thread-cert/node_cli.py b/tests/scripts/thread-cert/node_cli.py
index 0d54ec2e2..489ee5d6b 100644
--- a/tests/scripts/thread-cert/node_cli.py
+++ b/tests/scripts/thread-cert/node_cli.py
@@ -441,13 +441,17 @@ class otCli:
         return addrs
 
     def get_addr(self, prefix):
-        network = ipaddress.ip_network(unicode(prefix))
+        network = ipaddress.ip_network(u'%s' % str(prefix))
         addrs = self.get_addrs()
 
         for addr in addrs:
-            ipv6_address = ipaddress.ip_address(addr.decode("utf-8"))
+            if isinstance(addr, bytearray):
+                addr = bytes(addr)
+            elif isinstance(addr, str) and sys.version_info[0] == 2:
+                addr = addr.decode("utf-8")
+            ipv6_address = ipaddress.ip_address(addr)
             if ipv6_address in network:
-                return ipv6_address.exploded.encode('utf-8')
+                return ipv6_address.exploded
 
         return None
 
diff --git a/tests/scripts/thread-cert/simulator.py b/tests/scripts/thread-cert/simulator.py
index 0a0fc7367..54c884503 100644
--- a/tests/scripts/thread-cert/simulator.py
+++ b/tests/scripts/thread-cert/simulator.py
@@ -267,7 +267,7 @@ class VirtualTime:
             elif type == self.OT_SIM_EVENT_RADIO_SPINEL_WRITE:
                 assert not self._is_radio(addr)
                 radio_addr = self._to_radio_addr(addr)
-                if not self.devices.has_key(radio_addr):
+                if not radio_addr in self.devices:
                     self.awake_devices.add(radio_addr)
 
                 event = (event_time, self.event_sequence, radio_addr, self.OT_SIM_EVENT_UART_WRITE, datalen, data)
@@ -279,7 +279,7 @@ class VirtualTime:
             elif type == self.OT_SIM_EVENT_UART_WRITE:
                 assert self._is_radio(addr)
                 core_addr = self._to_core_addr(addr)
-                if not self.devices.has_key(core_addr):
+                if not core_addr in self.devices:
                     self.awake_devices.add(core_addr)
 
                 event = (event_time, self.event_sequence, core_addr, self.OT_SIM_EVENT_RADIO_SPINEL_WRITE, datalen, data)