python - siir.py unable to run -

i tried chris felton's myhdl sample code.

i not simulation module imported functions compile following errors:

traceback (most recent call last) file "siir.py", line 497, in <module> tb = flt.testfreqresponse(nloops=3, nfft=1024) file "siir.py", line 408, in testfreqresponse dut = tracesignals(self.rtl, clk, x, y, ts) file "c:\winpython-32bit-2.7.6.3\python-2.7.6\lib\site-   packages\myhdl\_tracesignals.py", line 82, in __call__ h = _hierextr(name, dut, *args, **kwargs) file "c:\winpython-32bit-2.7.6.3\python-2.7.6\lib\site- packages\myhdl\_extracthierarchy.py", line 233, in __init__ _top = dut(*args, **kwargs) file "siir.py", line 370, in rtl hdl = siir_hdl(clk, x, y, ts, a=self.fxa, b=self.fxb, w=self.w) file "siir.py", line 87, in siir_hdl assert len(a) == 3, "tuple of denominator coefficients length 3" assertionerror: tuple of denominator coefficients length 3 exception typeerror: 'isinstance() arg 2 must class, type, or tuple of classes ,   types' in  <generator object _labelgenerator @ 0x023add00> ignored 

could kindly advise i'm doing wrong? python 2.7 should ok? tried both file , python interactive command line.