Python: Error Handling

[last updated: 2019-11-01]
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• Errors are of several types:
• FileNotFound
• 'Type' something or other ...
• [something] not defined
• others ...
• Each error type must be handled/coded separately.
  While there may be other ways of doing it, the 'try' - 'except' structure works:
  

  try:
       [expressions]
  except [error type]:
       [expressions]

• However you can capture all error types with:
  ...
  except Exception:
• If you want to put the error message into a variable, eg. so you can print it, do this:
  ...
  except Exception as errorMsg:
       print(errorMsg)
• You can also investigate the exception errors using system parameters:
• sys.exc_info()
  This function returns a tuple of three values that give information about the exception that is currently being handled. If no exception is being handled anywhere on the stack, a tuple containing three None values is returned.
  Otherwise, the values returned are:
  (type, value, traceback).

  Their meaning is:

  'type' gets the exception type of the exception being handled (a class object);
  'value' gets the exception parameter (its associated value or the second argument to raise, which is always a class instance if the exception type is a class object);
  'traceback' gets a traceback object (see the Reference Manual) which encapsulates the call stack at the point where the exception originally occurred.

  If exc_clear() is called, this function will return three None values until either another exception is raised.

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