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Solve the following problem using Python, implementing the functions described below, one line at a time
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Description:
 def is_linear(self):
 """ Tests whether all filters in the list are linear. CascadeFilter and ParallelFilter instances are also linear if all filters they group are linear. """

    return all(isinstance(filt, LinearFilter) or
               (hasattr(filt, "is_linear") and filt.is_linear())
               for filt in self.callables)