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8.5 User-defined Exceptions

Programs may name their own exceptions by assigning a string to a variable. For example:

      >>> my_exc = 'my_exc'
      >>> try:
      ...     raise my_exc, 2*2
      ... except my_exc, val:
      ...     print 'My exception occurred, value:', val
      ...
      My exception occurred, value: 4
      >>> raise my_exc, 1
      Traceback (innermost last):
        File "<stdin>", line 1
      my_exc: 1

Many standard modules use this to report errors that may occur in functions they define.