In this troubleshooting session, I was met with a series of errors.

Challenge

On the Messages page, the list of message groups was not showing. This was caused by a combination of multiple error codes here and there. This post lists the problems and solutions in the chronological sequence.

1. Import error

[2023-05-03 09:00:12,427] ERROR in app: Exception on /api/message_groups [GET]
Traceback (most recent call last):
    ...
  File "/backend-flask/app.py", line 207, in data_message_groups
    model = MessageGroups.run(cognito_user_id=cognito_user_id)
NameError: name 'MessageGroups' is not defined
192.168.160.10 - - [03/May/2023 09:00:12] "GET /api/message_groups HTTP/1.1" 500 -

Reason: the module (import statement) was missing in the file app.py for some reason.

✅ Solution: import message_groups.py to app.py.

  from services.message_groups import *

2. Wrong parameter in the class MessagesGroups

[2023-05-03 09:08:27,784] ERROR in app: Exception on /api/message_groups [GET]
Traceback (most recent call last):
    ...
  File "/backend-flask/app.py", line 208, in data_message_groups
    model = MessageGroups.run(cognito_user_id=cognito_user_id)
TypeError: MessageGroups.run() got an unexpected keyword argument 'cognito_user_id'
192.168.160.10 - - [03/May/2023 09:08:27] "GET /api/message_groups HTTP/1.1" 500 -

Reason: when we update function's parameters, we often forget to update the function calls in other files.

✅ Updated the variable from user_handle to cognito_user_id.

  # from 
  class MessageGroups:
    def run(cognito_user_id):        
          ...

  # to 
    def run(cognito_user_id):        
          ...

3. Bad naming of variables

[2023-05-03 09:14:57,032] ERROR in app: Exception on /api/message_groups [GET]
Traceback (most recent call last):
    ...
  File "/backend-flask/app.py", line 208, in data_message_groups
    model = MessageGroups.run(cognito_user_id=cognito_user_id)
  File "/backend-flask/services/message_groups.py", line 29, in run
    ddb = ddb.client()
UnboundLocalError: local variable 'ddb' referenced before assignment

Reason: ddb is already the name of a python file and the class it contains. Silly enough, I named my ddb client variable as ddb which should be initialised by the class of the same name ddb (a single variable name had been used to refer to two different entities).

✅ Update the variables with different names. In below code, both the ddb client instance and the ddb class are called equally ddb.

  from lib.ddb import ddb  <----- 

  class MessageGroups:
    def run(cognito_user_id):
      ...
      ddb = ddb.client()   <---------- the problem 
      data = ddb.list_message_groups(ddb, current_user_uuid)

✅ Change like this:
- dynamodb \= ddb.client()
  
  data = ddb.list_message_groups(dynamodb, current_user_uuid)

4. Incorrectly referencing undefined variable

[2023-05-03 09:38:02,243] ERROR in app: Exception on /api/message_groups [GET]
Traceback (most recent call last):
    ...
  File "/backend-flask/app.py", line 208, in data_message_groups
    model = MessageGroups.run(cognito_user_id=cognito_user_id)
  File "/backend-flask/services/message_groups.py", line 33, in run
    model['data'] = results
NameError: name 'results' is not defined

Source code

class MessageGroups:
  def run(cognito_user_id):

    printh("MessageGroups.run ...")

    model = {
      'errors': None,  
      'data': None    <---- this becomes the chat room list on frontend.  
    }
    ...
    data = ddb.list_message_groups( ... )
    model['data'] = results           <----- 'results' was never defined.

    return model

Reason: accidentally, the word results was assigned as the value of model['data'] but results was never defined anywhere in the code.
✅ Simply replace it with the real variable with actual values data.

Resolved - End result

The message groups correctly displaying.

🔗NameError: name 'MessageGroups' is not defined