How to see exceptions raised from a channels consumer

I begin to use django-channels and I find it fantastic. However debugging consumers is painful because when some exceptions are raised from inside a consumer, nothing is printed to the terminal, the websocket is simply disconnected.

The kind of exception not shown is not obvious to identify. It is the case systematically for AssertionError, and also some others, for example the code below:

class MexicoProgressConsumer(ProgressConsumer):
    def init(self, SSDBConfig, Sub_application):
        subappli = models.Sub_application.objects.get(pk=Sub_application)
        ...

Calling this method with a wrong number of arguments does not print anything on the console and disconnect the websocket. Idem if the get on the last line fails.

Is there a way to see those exceptions as any other ones?

Solution

I found a solution to my problem. I first define a decorator:

import traceback
def catch_exception(f):
    def wrapper(*args, **kwargs):
        try:
            return f(*args, **kwargs)
        except StopConsumer:
            raise
        except Exception as e:
            print(traceback.format_exc().strip('\n'), '<--- from consumer')
            raise
    return wrapper

Then I define a base class for all my consumers, that uses this decorator this way:

import inspect
class BaseConsumer(JsonWebsocketConsumer):
    def __getattribute__(self, name):
        value = object.__getattribute__(self, name)
        if inspect.ismethod(value):
            return catch_exception(value)
        return value

But 2 problems persist:

Exceptions normally shown appear twice
Other exceptions are repeated 3 or 4 times! (as if each level of class hierarchy fires)

Exemple of the first case (KeyError):

Traceback (most recent call last):
  File "/home/alain/ADN/simutool/dbsimu/consumers.py", line 19, in wrapper
    return f(*args, **kwargs)
  File "/home/alain/ADN/simutool/dbsimu/consumers.py", line 31, in wrapper
    result = f(owner, **kwargs)
  File "/home/alain/ADN/simutool/dbsimu/consumers.py", line 110, in refresh
    data = super().refresh.__wrapped__(self)
  File "/home/alain/ADN/simutool/dbsimu/consumers.py", line 73, in refresh
    pvalue = round(data['toto'] * 100, 1)
KeyError: 'toto' <--- from consumer
Exception in thread Thread-3:
Traceback (most recent call last):
  File "/usr/lib/python3.6/threading.py", line 916, in _bootstrap_inner
    self.run()
  File "/usr/lib/python3.6/threading.py", line 864, in run
    self._target(*self._args, **self._kwargs)
  File "/home/alain/ADN/simutool/dbsimu/utils.py", line 193, in repeat
    self.repeat_func()
  File "/home/alain/ADN/simutool/dbsimu/consumers.py", line 19, in wrapper
    return f(*args, **kwargs)
  File "/home/alain/ADN/simutool/dbsimu/consumers.py", line 31, in wrapper
    result = f(owner, **kwargs)
  File "/home/alain/ADN/simutool/dbsimu/consumers.py", line 110, in refresh
    data = super().refresh.__wrapped__(self)
  File "/home/alain/ADN/simutool/dbsimu/consumers.py", line 73, in refresh
    pvalue = round(data['toto'] * 100, 1)
KeyError: 'toto'

Example of the second case (misspelled variable):

WebSocket CONNECT /ws/dbsimu/Simuflow_progress/ [127.0.0.1:55866]
Traceback (most recent call last):
  File "/home/alain/ADN/simutool/dbsimu/consumers.py", line 19, in wrapper
    return f(*args, **kwargs)
  File "/home/alain/ADN/simutool/dbsimu/consumers.py", line 57, in receive_json
    return getattr(self, icommand)(**data)
NameError: name 'icommand' is not defined <--- from consumer
Traceback (most recent call last):
  File "/home/alain/ADN/simutool/dbsimu/consumers.py", line 19, in wrapper
    return f(*args, **kwargs)
  File "/home/alain/.local/lib/python3.6/site-packages/channels/generic/websocket.py", line 125, in receive
    self.receive_json(self.decode_json(text_data), **kwargs)
  File "/home/alain/ADN/simutool/dbsimu/consumers.py", line 19, in wrapper
    return f(*args, **kwargs)
  File "/home/alain/ADN/simutool/dbsimu/consumers.py", line 57, in receive_json
    return getattr(self, icommand)(**data)
NameError: name 'icommand' is not defined <--- from consumer
Traceback (most recent call last):
  File "/home/alain/ADN/simutool/dbsimu/consumers.py", line 19, in wrapper
    return f(*args, **kwargs)
  File "/home/alain/.local/lib/python3.6/site-packages/channels/generic/websocket.py", line 60, in websocket_receive
    self.receive(text_data=message["text"])
  File "/home/alain/ADN/simutool/dbsimu/consumers.py", line 19, in wrapper
    return f(*args, **kwargs)
  File "/home/alain/.local/lib/python3.6/site-packages/channels/generic/websocket.py", line 125, in receive
    self.receive_json(self.decode_json(text_data), **kwargs)
  File "/home/alain/ADN/simutool/dbsimu/consumers.py", line 19, in wrapper
    return f(*args, **kwargs)
  File "/home/alain/ADN/simutool/dbsimu/consumers.py", line 57, in receive_json
    return getattr(self, icommand)(**data)
NameError: name 'icommand' is not defined <--- from consumer

If somebody has any idea to fix that, please advise.