Simple Python struct issue

[Carlo DiCelico]

I saw an article on O'Reilly about using NumPy and Dislin to analyze
and visualize WAV files. It's a really fantastic article but was a
little out of date. I updated the script to work with the newer
modules &etc but am still having trouble getting it working.

The line

temp[i,:] = array(struct.unpack("%dB"%(fft_length), tempb),Float) -
128.0

always returns the same error: "Traceback (most recent call last):
  File "pysono.py", line 31, in <module>
   temp[i,:] = array(struct.unpack("%dB"%(fft_length),tempb),float) -
128.0
struct.error: unpack requires a string argument of length 256" when I
do python pysono.py test.wav 256

I'm sure it's probably something simple but I just can't see what it
is!

Here's the original code: http://onlamp.com/python/2001/01/31/graphics/pysono.py

Thanks!