[Python] fix api file name & api var name (#11051)

* fix api filename

* fix PythonCodeGen toApiVarName

* add samples change

samples/client/petstore/python-asyncio/test/test_fake_classname_tags123_api.py

@@ -0,0 +1,40 @@
+# coding: utf-8
+
+"""
+    OpenAPI Petstore
+
+    This spec is mainly for testing Petstore server and contains fake endpoints, models. Please do not use this for any other purpose. Special characters: \" \\  # noqa: E501
+
+    The version of the OpenAPI document: 1.0.0
+    Generated by: https://openapi-generator.tech
+"""
+
+
+from __future__ import absolute_import
+
+import unittest
+
+import petstore_api
+from petstore_api.api.fake_classname_tags_123_api import FakeClassnameTags123Api  # noqa: E501
+from petstore_api.rest import ApiException
+
+
+class TestFakeClassnameTags123Api(unittest.TestCase):
+    """FakeClassnameTags123Api unit test stubs"""
+
+    def setUp(self):
+        self.api = petstore_api.api.fake_classname_tags_123_api.FakeClassnameTags123Api()  # noqa: E501
+
+    def tearDown(self):
+        pass
+
+    def test_test_classname(self):
+        """Test case for test_classname
+
+        To test class name in snake case  # noqa: E501
+        """
+        pass
+
+
+if __name__ == '__main__':
+    unittest.main()