Subclass Python exceptions (#7321)

* Subclass Python exceptions:
- UnauthorizedException (401)
- ForbiddenException (403)
- NotFoundException (404)
- ServiceException [500 - 599]

Fixes #2151

* add generated sample code

* use Python 2 flavor inheritance

* regenerate samples

samples/client/petstore/python-asyncio/petstore_api/exceptions.py

@@ -128,6 +128,30 @@ class ApiException(OpenApiException):
         return error_message
 
 
+class NotFoundException(ApiException):
+
+    def __init__(self, status=None, reason=None, http_resp=None):
+        super(NotFoundException, self).__init__(status, reason, http_resp)
+
+
+class UnauthorizedException(ApiException):
+
+    def __init__(self, status=None, reason=None, http_resp=None):
+        super(UnauthorizedException, self).__init__(status, reason, http_resp)
+
+
+class ForbiddenException(ApiException):
+
+    def __init__(self, status=None, reason=None, http_resp=None):
+        super(ForbiddenException, self).__init__(status, reason, http_resp)
+
+
+class ServiceException(ApiException):
+
+    def __init__(self, status=None, reason=None, http_resp=None):
+        super(ServiceException, self).__init__(status, reason, http_resp)
+
+
 def render_path(path_to_item):
     """Returns a string representation of a path"""
     result = ""