Custom Python Exceptions with Error Codes and Error Messages

Question

class AppError(Exception):
    pass

class MissingInputError(AppError):
    pass

class ValidationError(AppError):
    pass

...

def v         


        

Answer 1

This is an example of a custom exception I created which makes use of pre-defined error codes:

class CustomError(Exception):
"""
Custom Exception
"""

  def __init__(self, error_code, message='', *args, **kwargs):

      # Raise a separate exception in case the error code passed isn't specified in the ErrorCodes enum
      if not isinstance(error_code, ErrorCodes):
          msg = 'Error code passed in the error_code param must be of type {0}'
          raise CustomError(ErrorCodes.ERR_INCORRECT_ERRCODE, msg, ErrorCodes.__class__.__name__)

      # Storing the error code on the exception object
      self.error_code = error_code

      # storing the traceback which provides useful information about where the exception occurred
      self.traceback = sys.exc_info()

      # Prefixing the error code to the exception message
      try:
          msg = '[{0}] {1}'.format(error_code.name, message.format(*args, **kwargs))
      except (IndexError, KeyError):
          msg = '[{0}] {1}'.format(error_code.name, message)

      super().__init__(msg)


# Error codes for all module exceptions
@unique
class ErrorCodes(Enum):
    ERR_INCORRECT_ERRCODE = auto()      # error code passed is not specified in enum ErrorCodes
    ERR_SITUATION_1 = auto()            # description of situation 1
    ERR_SITUATION_2 = auto()            # description of situation 2
    ERR_SITUATION_3 = auto()            # description of situation 3
    ERR_SITUATION_4 = auto()            # description of situation 4
    ERR_SITUATION_5 = auto()            # description of situation 5
    ERR_SITUATION_6 = auto()            # description of situation 6

The enum ErrorCodes is used to define error codes. The exception is created in such a way that the error code passed is prefixed to the exception message.