Hi, I noticed the following behaviour for empty lists: In [4]: N.median([]) --------------------------------------------------------------------------- exceptions.IndexError Traceback (most recent call last) /home/stefan/<ipython console> /home/stefan/lib/python2.4/site-packages/numpy/lib/function_base.py in median(m) 1081 return sorted[index] 1082 else: -> 1083 return (sorted[index-1]+sorted[index])/2.0 1084 1085 def trapz(y, x=None, dx=1.0, axis=-1): IndexError: index out of bounds In [5]: N.mean([]) Out[5]: nan In [6]: N.average([]) --------------------------------------------------------------------------- exceptions.ZeroDivisionError Traceback (most recent call last) /home/stefan/<ipython console> /home/stefan/lib/python2.4/site-packages/numpy/lib/function_base.py in average(a, axis, weights, returned) 294 if not isinstance(d, ndarray): 295 if d == 0.0: --> 296 raise ZeroDivisionError, 'zero denominator in average()' 297 if returned: 298 return n/d, d ZeroDivisionError: zero denominator in average() Which is the ideal response -- NaN or an exception, and if an exception, of which kind? Cheers Stéfan