Distributed system: Raise error thrown on server side on client side

Question

I have just started to create a distributed system that now got a single server and a bunch of clients. The language used is python and communication is done using sockets and JSON. When an error occurs on the server-side I send the error class-name and the error arguments to the client-side like this:

     except Exception as e:
         jsonResult = {"error":                                                                                 
                       {   
                           "name":e.__class__.__name__,                                                         
                           "args": e.args                                                                       
                       }                                                                                        
         }                                                                                                      

         jsonResult = json.dumps(jsonResult)                                                                    
         jsonResult += "\n"                                                                                     

         return jsonResult

And then try to raise it on the client-side like this:

          errorFunc = decodedReply["error"]["name"]
          args = decodedReply["error"]["args"]
          print (args)

          # Builds and appends the argumentstring to the error class-name.
          errorFunc += '('
          for arg in args:
              # Handles when the argument is a string.
              if isinstance(arg, str):
                  errorFunc += '\'' + arg + '\','
              else:
                  errorFunc += arg + ','

          # Removes the extra ',' from the string before adding the last ')'. 
          errorFunc = errorFunc[:-1] 
          errorFunc += ')'

          # Debugging print.
          print ("Here: " + errorFunc)

          raise exec(errorFunc)

When I do this I get the error

TypeError: exceptions must derive from BaseException

From what I read here: Error exception must derive from BaseException even when it does (Python 2.7)

it looks like I have to declare it as a class. Is there anyway to get around that?

`Here: ValueError('ABC')` is the output. The error is one I have raised manually on the server-side. — B.Jansson, Feb 01 '17 at 11:07

score 1 · Accepted Answer · answered Feb 01 '17 at 11:10

According to python you are raising something which is not an exception:

>>> type(exec("ValueError('ABC')"))
<class 'NoneType'>

You need to rewrite your code to have this:

>>> errorFunc = "ValueError('ABC')"
>>> exec('raise ' + errorFunc)
Traceback (most recent call last):
  File "<stdin>", line 1, in <module>
  File "<string>", line 1, in <module>
ValueError: ABC

Distributed system: Raise error thrown on server side on client side

1 Answers1