[VXLAN]Fixing traceback in show remotemac when mac moves during command execution (sonic-net#2506)

- What I did
During the execution of show vxlan remotemac command, if a mac moves after the key is fetched but not the table fields, there will be the below traceback

show vxlan remotemac 2.2.2.2 
This is because the entry would have got removed before the CLI fetches the table.

- How I did it
Used get API to fetch table rather than indexing directly which resulted in traceback. Additionally fixed Python 3.8 SyntaxWarning.

show vxlan remotemac all
/usr/local/lib/python3.9/dist-packages/show/vxlan.py:101: SyntaxWarning: "is not" with a literal. Did you mean "!="?
if vtep_sip is not '0.0.0.0':
/usr/local/lib/python3.9/dist-packages/show/vxlan.py:108: SyntaxWarning: "is not" with a literal. Did you mean "!="?
if vtep_sip is not '0.0.0.0':

- How to verify it
Perform mac move during show command execution and verify there is no traceback.

Author: dgsudharsan

show/vxlan.py

@@ -98,14 +98,14 @@ def interface():
           vtepname = key1.pop();
           if 'src_ip' in vxlan_table[key]:
             vtep_sip = vxlan_table[key]['src_ip']
-          if vtep_sip is not '0.0.0.0':
+          if vtep_sip != '0.0.0.0':
              output = '\tVTEP Name : ' + vtepname + ', SIP  : ' + vxlan_table[key]['src_ip']
           else:
              output = '\tVTEP Name : ' + vtepname
 
           click.echo(output)
 
-    if vtep_sip is not '0.0.0.0':
+    if vtep_sip != '0.0.0.0':
        vxlan_table = config_db.get_table('VXLAN_EVPN_NVO')
        vxlan_keys = vxlan_table.keys()
        if vxlan_keys is not None:
@@ -307,8 +307,8 @@ def remotemac(remote_vtep_ip, count):
             vxlan_table = db.get_all(db.APPL_DB, key);
             if vxlan_table is None:
              continue
-            rmtip = vxlan_table['remote_vtep']
-            if remote_vtep_ip != 'all' and rmtip != remote_vtep_ip:
+            rmtip = vxlan_table.get('remote_vtep')
+            if remote_vtep_ip != 'all' and rmtip != remote_vtep_ip or rmtip is None:
                continue
             if count is None:
                body.append([vlan, mac, rmtip, vxlan_table['vni'], vxlan_table['type']])

tests/mock_tables/appl_db.json

@@ -290,6 +290,16 @@
     "VXLAN_REMOTE_VNI_TABLE:Vlan200:25.25.25.27": {
         "vni": "200"
     },
+    "VXLAN_FDB_TABLE:Vlan200:00:02:00:00:47:e2": {
+        "remote_vtep": "2.2.2.2",
+        "type": "dynamic",
+        "vni": "200"
+    },
+    "VXLAN_FDB_TABLE:Vlan200:00:02:00:00:47:e3": {
+        "remote_vtep": "2.2.2.3",
+        "type": "dynamic",
+        "vni": "200"
+    },
     "MUX_CABLE_TABLE:Ethernet32": {
         "state": "active"
     },

tests/vxlan_test.py

@@ -112,6 +112,38 @@
 
 """
 
+show_vxlan_remotemac_all_output="""\
++---------+-------------------+--------------+-------+---------+
+| VLAN    | MAC               | RemoteVTEP   |   VNI | Type    |
++=========+===================+==============+=======+=========+
+| Vlan200 | 00:02:00:00:47:e2 | 2.2.2.2      |   200 | dynamic |
++---------+-------------------+--------------+-------+---------+
+| Vlan200 | 00:02:00:00:47:e3 | 2.2.2.3      |   200 | dynamic |
++---------+-------------------+--------------+-------+---------+
+Total count : 2
+
+"""
+
+show_vxlan_remotemac_specific_output="""\
++---------+-------------------+--------------+-------+---------+
+| VLAN    | MAC               | RemoteVTEP   |   VNI | Type    |
++=========+===================+==============+=======+=========+
+| Vlan200 | 00:02:00:00:47:e2 | 2.2.2.2      |   200 | dynamic |
++---------+-------------------+--------------+-------+---------+
+Total count : 1
+
+"""
+
+show_vxlan_remotemac_cnt_output="""\
+Total count : 2
+
+"""
+
+show_vxlan_remotemac_specific_cnt_output="""\
+Total count : 1
+
+"""
+
 class TestVxlan(object):
     @classmethod
     def setup_class(cls):
@@ -215,6 +247,38 @@ def test_show_vxlan_remotevni_specific_cnt(self):
         assert result.exit_code == 0
         assert result.output == show_vxlan_remotevni_specific_cnt_output
 
+    def test_show_vxlan_remotemac(self):
+        runner = CliRunner()
+        result = runner.invoke(show.cli.commands["vxlan"].commands["remotemac"], ["all"])
+        print(result.exit_code)
+        print(result.output)
+        assert result.exit_code == 0
+        assert result.output == show_vxlan_remotemac_all_output
+
+    def test_show_vxlan_remotemac_specific(self):
+        runner = CliRunner()
+        result = runner.invoke(show.cli.commands["vxlan"].commands["remotemac"], ["2.2.2.2"])
+        print(result.exit_code)
+        print(result.output)
+        assert result.exit_code == 0
+        assert result.output == show_vxlan_remotemac_specific_output
+
+    def test_show_vxlan_remotemac_cnt(self):
+        runner = CliRunner()
+        result = runner.invoke(show.cli.commands["vxlan"].commands["remotemac"], ["all", "count"])
+        print(result.exit_code)
+        print(result.output)
+        assert result.exit_code == 0
+        assert result.output == show_vxlan_remotemac_cnt_output
+
+    def test_show_vxlan_remotemac_specific_cnt(self):
+        runner = CliRunner()
+        result = runner.invoke(show.cli.commands["vxlan"].commands["remotemac"], ["2.2.2.2", "count"])
+        print(result.exit_code)
+        print(result.output)
+        assert result.exit_code == 0
+        assert result.output == show_vxlan_remotemac_specific_cnt_output
+
     def test_config_vxlan_add(self):
         runner = CliRunner()
         db = Db()