Handy FIR filter inherits from list:

   class filter(list):

   """real valued F I R filter with memory"""

   def __init__(self, coeffs, data=None):
            list.__init__([float(item) for item in coeffs])
       if data:
           assert len(data) == len(coeffs)
           self.data =[float(datum) for datum in data]
       else:
           self.data = len(self) * [0.]

   def __call__(self,value=0.):
       return self.filter(value)

   def output(self):
       return sum(map(mul, self.coeffs, self.data))

   def update(self,value):
       self.pop(0)
       self.append(value)

   def filter(self, value=0.):
       value = float(value)
       self.update(value)
       return self.output()

   def innovate(self):
       return self.filter(white())