Exception Handling

Python and C have quite different ways of reporting errors. In Python exceptions are raised (and possibly caught) whenever an error occurs. In C a function will typically return an error value, such as -1 or NULL.

XOSD

To raise a Python exception you have to check the return value when you call the function. For example, the following modification of the __new__ method we wrote earlier raises SomeKindOfExcpetion if xosd_create returns NULL.

  def __new__(self, font, colour):
    self.xosdWin = xosd_create(1)
    if (self.xosdWin == NULL):
      msg = 'xosd_create returned NULL'
      raise SomeKindOfException(msg)
    xosd_set_font(self.xosdWin, font)
    xosd_set_colour(self.xosdWin, colour)

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